JP3556655B2 - Liquid crystal display - Google Patents

Description

【００３３】
の関係を満たすように設定されている。
【００３４】
第２の液晶表示装置では、上記液晶層における液晶材料の、波長６５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （６５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （５５０）の比であるΔｎ_Ｌ （６５０）／Δｎ_Ｌ （５５０）と、上記光学位相差板の波長６５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （６５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （５５０）の比であるΔｎ_Ｆ （６５０）／Δｎ_Ｆ （５５０）とが、
【００３５】
【数６】

【００３６】
の関係を満たすように設定されている。
【００３７】
上記構成によれば、主屈折率ｎ_ａ 、ｎ_ｂ 、ｎ_ｃ がｎ_ａ ＝ｎ_ｃ ＞ｎ_ｂ という関係にあり、主屈折率ｎ_ｂ を含む屈折率楕円体の短軸を光学位相差板の表面の法線方向に対し傾斜させた光学位相差板が液晶層と偏光子との間に介在されているので、直線偏光が複屈折性を有する液晶層を通過して、正常光と異常光とが発生し、これらの位相差に伴って楕円偏光に変換される場合、視角に応じて生ずる正常光と異常光との位相差変化がこの光学位相差板によって補償される。
【００３８】
しかしながら、このような補償機能によっても、さらなる視角依存性の改善が要求されるなかでは必ずしも充分であるとは言えず、本願発明者らは、さらなる研究を重ねた結果、上記液晶層における液晶材料の屈折率異方性Δｎの光の波長に対する変化と、上記光学位相差板の屈折率異方性Δｎの光の波長に対する変化との変化度合が、視角に依存した液晶画面の着色に影響することを見い出し、本発明を完成させるに至った。
【００３９】
液晶層における液晶材料の屈折率異方性Δｎの光の波長に対する変化を、上記第１、第２の液晶表示装置において記載した何れかの範囲とすることで、通常の液晶表示装置にて要求される視角５０°において、若干の色付きはあるものの、どの方向から見ても充分に使用に耐えうるものとでき、画面の着色をより一層防止することが可能となった。尚、コントラスト変化や反転現象においても、位相差板の補償機能のみの場合よりも、改善することができた。
【００４０】
そして、視角７０°といったさらに広視野角の液晶表示装置においては、液晶材料の屈折率異方性Δｎの光の波長に対する変化の範囲を、以下の範囲とすることが好ましい。
【００４１】
即ち、
【００４２】
【数７】

【００４３】
の関係を満たすように設定する。
【００４４】
または、
【００４５】
【数８】

【００４６】
の関係を満たすように設定する。
【００４７】
これらの何れかの範囲とすることで、広視野角の液晶表示装置にて要求される視角７０°においてあらゆる方向から見ても、全く着色現象のないものとできる。
【００４８】
また、上記した本発明の各液晶表示装置においては、液晶層における液晶材料の、波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）を、０．０６０より大きく０．１２０より小さい範囲に設定することが好ましい。
【００４９】
これは、可視光領域の中心領域となる波長５５０ｎｍの光に対する液晶材料の屈折率異方性Δｎ（５５０）が０．０６０以下または０．１２０以上の場合、視角方向によっては反転現象やコントラスト比の低下が発生することが確認されたためである。そこで、液晶材料の波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）を、０．０６０より大きく０．１２０より小さい範囲に設定することにより、液晶表示素子に生じる視角に対応する位相差を解消することができるため、液晶画面において、視角に依存して生じる着色現象はもちろんのこと、コントラスト変化、左右方向の反転現象等もさらに改善することができる。
【００５０】
この場合、さらに、液晶層における液晶材料の、波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）を、０．０７０以上０．０９５以下の範囲に設定することで、液晶表示素子に生じる視角に対応する位相差をより効果的に解消することができるため、液晶表示画像におけるコントラスト変化、左右方向の反転現象を確実に改善することができる。
【００５１】
また、上記した本発明の各液晶表示装置においては、全ての光学位相差板において、屈折率楕円体の傾斜角が１５°から７５°の間に設定されていることが好ましい。
【００５２】
このように、液晶表示装置に介在される全ての光学位相差板において、屈折率楕円体の傾斜角を１５°から７５°の間に設定することで、前述した本発明の備えた光学位相差板による位相差の補償機能を確実に得ることができる。
【００５３】
また、上記した本発明の各液晶表示装置においては、全ての光学位相差板において、主屈折率ｎ_ａ と主屈折率ｎ_ｂ との差と、光学位相差板の厚さｄとの積（ｎ_ａ −ｎ_ｂ ）×ｄが、８０ｎｍから２５０ｎｍの間に設定されていることが好ましい。
【００５４】
このように、液晶表示装置に介在される全ての光学位相差板において、主屈折率ｎ_ａ と主屈折率ｎ_ｂ との差と、光学位相差板の厚さｄとの積（ｎ_ａ −ｎ_ｂ ）×ｄを、８０ｎｍから２５０ｎｍの間に設定することで、前述した本発明の備えた光学位相差板による位相差の補償機能を確実に得ることができる。
【００５５】
【発明の実施の形態】
本発明の実施の一形態について図１ないし図１０に基づいて説明すれば、以下の通りである。
【００５６】
まず、本発明の実施の形態を説明する前に、参考例の液晶表示装置について説明する。この液晶表示装置は、図１に示すように、液晶表示素子１と、一対の光学位相差板２・３と、一対の偏光板（偏光子）４・５とを備えている。
【００５７】
液晶表示素子１は、対向して配される電極基板６・７の間に液晶層８を挟む構造をなしている。電極基板６は、ベースとなるガラス基板（透光性基板）９の液晶層８側の表面にＩＴＯ（インジウム錫酸化物）からなる透明電極１０が形成され、その上に配向膜１１が形成されている。電極基板７は、ベースとなるガラス基板（透光性基板）１２の液晶層８側の表面にＩＴＯからなる透明電極１３が形成され、その上に配向膜１４が形成されている。
【００５８】
簡略化のため、図１は２画素分の構成を示しているが、液晶表示素子１の全体において、所定幅の帯状の透明電極１０・１３は、ガラス基板９・１２のそれぞれに所定間隔をおいて配され、かつ、ガラス基板９・１２間では基板面に垂直な方向から見て相互に直交するように形成されている。両透明電極１０・１３が交差する部分は表示を行う画素に相当し、これらの画素は液晶表示装置の全体においてマトリクス状に配設されている。
【００５９】
電極基板６・７は、シール樹脂１５により貼り合わされており、電極基板６・７とシール樹脂１５とによって形成される空間内に液晶層８が封入されている。液晶層８には、透明電極１０・１３を介して、駆動回路（電圧印加手段）１７より表示データに基づいた電圧が印加される。
【００６０】
尚、詳細については後述するが、本液晶表示装置においては、光学位相差板２・３による位相差の補償機能と最良な特性を有する組み合わせとなるように、上記液晶層８のプレティルト角が設定されている。
【００６１】
液晶表示装置において、上記の液晶表示素子１に光学位相差板２・３と偏光板４・５とが形成されてなるユニットが液晶セル１６である。
【００６２】
配向膜１１・１４は、介在する液晶分子が約９０°の捻じれ配向となるように、予めラビング処理が施されている。図２に示すように、配向膜１１のラビング方向Ｒ１と配向膜１４のラビング方向Ｒ２とは、互いに直交する方向に設定されている。
【００６３】
光学位相差板２・３は、液晶表示素子１とその両側に配される偏光板４・５との間にそれぞれ介在される。光学位相差板２・３は、透明な有機高分子からなる支持体にディスコティック液晶が傾斜配向またはハイブリッド配向され、かつ架橋されることにより形成されている。これにより、光学位相差板２・３における後述の屈折率楕円体が、光学位相差板２・３に対して傾斜するように形成される。
【００６４】
光学位相差板２・３の支持体としては、一般に偏光板によく用いられるトリアセチルセルロース（ＴＡＣ）が信頼性も高く適している。それ以外では、ポリカーボネート（ＰＣ）、ポリエチレンテレフタレート（ＰＥＴ）などの耐環境性や耐薬品性に優れた無色透明の有機高分子フィルムが適している。
【００６５】
図３に示すように、光学位相差板２・３は、異なる３方向の主屈折率ｎ_ａ ・ｎ_ｂ ・ｎ_ｃ を有している。主屈折率ｎ_ａ の方向は、互いに直交座標ｘｙｚにおける各座標軸のうちｙ座標軸と方向が一致している。主屈折率ｎ_ｂ の方向は、光学位相差板２・３において画面に対応する表面に垂直なｚ座標軸（表面の法線方向）に対し矢印Ａの方向にθ傾いている。
【００６６】
光学位相差板２・３は、各主屈折率がｎ_ａ ＝ｎ_ｃ ＞ｎ_ｂ という関係を満たしている。これにより、光学軸が１つのみ存在するので、光学位相差板２・３は一軸性を備え、また、屈折率異方性が負になる。光学位相差板２・３の第１のリタデーション値（ｎ_ｃ −ｎ_ａ ）×ｄは、ｎ_ａ ＝ｎ_ｃ であるため、ほぼ０ｎｍである。第２のリタデーション値（ｎ_ｃ −ｎ_ｂ ）×ｄは、８０ｎｍ〜２５０ｎｍの範囲内で任意の値に設定される。第２のリタデーション値（ｎ_ｃ −ｎ_ｂ ）×ｄをこのような範囲内に設定することで、光学位相差板２・３による位相差の補償機能を確実に得ることができる。尚、上記のｎ_ｃ −ｎ_ａ およびｎ_ｃ −ｎ_ｂ は屈折率異方性Δｎを表し、ｄは光学位相差板２・３の厚みを表している。
【００６７】
また、光学位相差板２・３の主屈折率ｎ_ｂ が傾いている角度θ、即ち、屈折率楕円体の傾斜角度θは、１５°≦θ≦７５°の範囲内で任意の値に設定される。傾斜角度θをこのような範囲内に設定することで、屈折率楕円体の傾斜の方向が時計回り反時計回りに係わらず、光学位相差板２・３による位相差の補償機能を確実に得ることができる。
【００６８】
尚、光学位相差板２・３の配置については、光学位相差板２・３のうちの何れか一方のみを片側に配置した構成でも、また、光学位相差板２・３を片側に重ねて配置することもできる。さらに、３枚以上の光学位相差板を用いることもできる。
【００６９】
そして、図４に示すように、参考例の液晶表示装置においては、液晶表示素子１における偏光板４・５は、その吸収軸ＡＸ_１ ・ＡＸ_２ が前記の配向膜１１・１４（図１参照）のラビング方向Ｒ_１ ・Ｒ_２ とそれぞれ平行となるように配置される。本液晶表示装置では、ラビング方向Ｒ_１ ・Ｒ_２ が互いに直交しているため、吸収軸ＡＸ_１ ・ＡＸ_２ も互いに直交している。
【００７０】
ここで、図３に示すように、光学位相差板２・３に異方性を与える方向に傾斜する主屈折率ｎ_ｂ の方向が光学位相差板２・３の表面に投影された方向をＤと定義する。図４に示すように、光学位相差板２は方向Ｄ（方向Ｄ_１ ）がラビング方向Ｒ_１ と平行になるように配され、光学位相差板３は方向Ｄ（方向Ｄ_２ ）がラビング方向Ｒ_２ と平行になるように配される。
【００７１】
上記のような光学位相差板２・３および偏光板４・５の配置により、本液晶表示装置は、オフ時において光を透過して白色表示を行ういわゆるノーマリホワイト表示を行う。
【００７２】
一般に、液晶や光学位相差板（位相差フィルム）といった光学異方体においては、上記のような３次元方向の主屈折率ｎ_ａ ・ｎ_ｃ ・ｎ_ｂ の異方性が屈折率楕円体で表される。屈折率異方性Δｎは、この屈折率楕円体をどの方向から観察するかによって異なる値になる。
【００７３】
次に、前述した、液晶層８におけるプレティルト角の設定について詳細に説明する。
【００７４】
プレティルト角とは、図５に示すように、液晶分子２０の長軸と配向膜１４（１１）とがなす角ψのことであり、配向膜１１・１４に対するラビングと、液晶材料との組み合わせによって決定されるものである。
【００７５】
前述したように、参考例の液晶表示装置では、光学位相差板２・３による位相差の補償機能と最良な特性を有する組み合わせとなるように、上記液晶層８のプレティルト角が設定されており、詳細に言えば、このプレティルト角が、液晶の閾値電圧に近い電圧を液晶に印加した中間調表示状態、ここではノーマリホワイト表示であるので白に近い中間調表示状態で、反視角方向の階調反転が発生しない範囲に設定されている。以下、白に近い中間調を白階調と呼ぶ。
【００７６】
一方、プレティルト角は大きくするほど、白階調時の反視角方向の階調反転が起こらなくなることが実験的に確認されたが、その反面、プレティルト角を大きくし過ぎると、正視角方向での白階調時の輝度の急激な低下が発生することも確認された。つまり、プレティルト角の設定には、白階調時に正視角方向の急激な輝度低下が発生しない範囲とすることも必要となる。
【００７７】
具体的には、配向膜１１・１４及び液晶材料として、プレティルト角が２°より大きく１２°未満の範囲となるような配向膜と液晶材料との組み合わせが用いられている。この場合、より好ましくは、プレティルト角が４°以上１０°以下の範囲となるような配向膜と液晶材料との組み合わせとすることである。
【００７８】
このようにプレティルト角を２°より大きく１２°未満の範囲内に設定することで、通常の液晶表示装置にて要求される視角５０°において、問題となるような白階調時の反視角方向の階調反転のない、どの方向から見ても充分に使用に耐え得るものとできる。
【００７９】
そして特に、プレティルト角を４°以上１０°以下の範囲内に設定することで、視角７０°において、白階調時の反視角方向の階調反転の全く無いものとできる。
【００８０】
さらに、参考例の液晶表示装置では、液晶層８における液晶材料として、波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）が、０．０６０より大きく０．１２０より小さい範囲に設計されたものが選択されている。この場合、より好ましくは、上記Δｎ（５５０）が、０．０７０以上０．０９５以下の範囲に設計された液晶材料を用いることである。
【００８１】
これにより、光学位相差板２・３による位相差の補償機能、及びプレティルト角を上記の範囲に設定したことによる補償機能に加えて、反視角方向のコントラスト比の低下、左右方向の反転現象をより一層改善することが可能となる。
【００８２】
以上のように、参考例の液晶表示装置は、液晶表示素子１と偏光板４・５の間に、屈折率楕円体の３つの主屈折率ｎ_ａ 、ｎ_ｂ 、ｎ_ｃ がｎ_ａ ＝ｎ_ｃ ＞ｎ_ｂ という関係を有し、表面内の主屈折率ｎ_ａ またはｎ_ｃ の方向を軸として、表面の法線方向に平行な主屈折率ｎ_ｂ の方向と、表面内の主屈折率ｎ_ｃ またはｎ_ａ の方向とが時計まわり、または反時計まわりに傾斜することにより、上記屈折率楕円体が傾斜している光学位相差板２・３を備えた構成の液晶表示装置において、液晶層８におけるプレティルト角を、液晶の閾値電圧に近い電圧を液晶に印加した中間調表示状態で、反視角方向の階調反転が発生しない範囲に設定した構成である。
【００８３】
これにより、液晶表示素子１に生じる視角に対応する位相差の上記の光学位相差板２・３による補償機能と共に、プレティルト角を上記の範囲に設定したことによる補償機能により、視角に依存した反視角方向の白階調時（ノーマリホワイト表示であるので）に発生する反転現象を特に効果的に改善することが可能であり、同時に、コントラスト変化も改善して、高品質の画像を表示できる。
【００８４】
しかも、この液晶表示装置では、液晶層８における液晶材料として、波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）が、０．０６０より大きく０．１２０より小さい範囲に設計されたものを用いているので、光学位相差板２・３による位相差の補償機能、及びプレティルト角を上記の範囲に設定したことによる補償機能に加えて、反視角方向のコントラスト比の低下、左右方向の反転現象をより一層改善することが可能となる。
【００８５】
なお、ここでは、ノーマリホワイト表示の液晶表示装置を例示して説明したが、ノーマリブラック表示の液晶表示装置においても、光学位相差板２・３による補償効果に合わせて、プレティルト角を液晶の閾値電圧に近い電圧を液晶に印加した中間調表示（黒階調）で反視角方向の階調反転が発生しない範囲に設定し、これによる補償効果を得ることで、上記と同様の効果を得ることができる。
【００８６】
また、ここでは、単純マトリクス方式の液晶表示装置について述べたが、本発明は、これ以外に、ＴＦＴなどの能動スイッチング素子を用いたアクティブマトリクス方式の液晶表示装置についても適用が可能である。
【００８７】
次に、他の参考例の液晶表示装置について、図１に基づいて説明する。尚、説明の便宜上、前述した参考例（以下、第１の参考例）の液晶表示装置にて示した部材と同一の機能を有する部材には、同一の符号を付記し、その説明を省略する。
【００８８】
ここで説明する第２の参考例の液晶表示装置は、前述した第１の参考例である図１の液晶表示装置とほぼ同様の構成を有している。異なる点は、第１の参考例の液晶表示装置では、光学位相差板２・３による位相差の補償機能と最良な特性を有する組み合わせとなるように、上記液晶層８のプレティルト角が、液晶層８に液晶の閾値電圧に近い電圧を印加した中間調表示状態で反視角方向の階調反転が発生しない範囲に設定されていたのに対し、第２の参考例の液晶表示装置では、光学位相差板２・３による位相差の補償機能と最良な特性を有する組み合わせとなるように、液晶層８に液晶の閾値電圧に近い電圧を印加することで得られる中間調を表示するための印加電圧値を、当該中間調の表示状態で反視角方向の階調反転が発生しない範囲に設定している点である。
【００８９】
以下、この点を詳細に説明する。第２の参考例の液晶表示装置は、ノーマリホワイト表示であるので、液晶の閾値電圧に近い電圧を液晶に印加した中間調表示状態、即ち、白階調を行うための印加電圧値が、該電圧を印加した状態で反視角方向の階調反転が発生しない範囲に設定されている。
【００９０】
一方、白階調時の透過率を下げるほど、白階調時の反視角方向の階調反転が起こらなくなることが実験的に確認されたが、その反面、透過率を低く設定し過ぎると、正視角方向、左右方向で輝度が急激に低下してしまう。つまり、白階調時の透過率を決定する液晶印加電圧の設定には、白階調時に正視角方向、左右方向の急激な輝度低下が発生しない範囲に設定することも必要となる。
【００９１】
具体的には、白階調時における液晶印加電圧が、液晶印加電圧がゼロのオフ状態の透過率１００％に対して８５％より大きい透過率を得るように設定されている。この場合、より好ましくは、白階調時における液晶印加電圧を、オフ状態の透過率１００％に対して９０％以上９７％以下の範囲に入る透過率を得るように設定することである。
【００９２】
このように白階調時の液晶印加電圧をオフ状態の透過率１００％に対して８５％より大きい透過率を得るように設定することで、通常の液晶表示装置にて要求される視角５０°において、問題となるような白階調時の反視角方向の階調反転のない、どの方向から見ても充分に使用に耐え得るものとできる。
【００９３】
そして特に、白階調時の液晶印加電圧をオフ状態の透過率１００％に対して９０％以上９７％以下の範囲に設定することで、視角７０°において、白階調時の反視角方向の階調反転の全く無いものとできる。
【００９４】
即ち、第２の参考例の液晶表示装置は、液晶表示素子１と偏光板４・５の間に、屈折率楕円体の３つの主屈折率ｎ_ａ 、ｎ_ｂ 、ｎ_ｃ がｎ_ａ ＝ｎ_ｃ ＞ｎ_ｂ という関係を有し、表面内の主屈折率ｎ_ａ またはｎ_ｃ の方向を軸として、表面の法線方向に平行な主屈折率ｎ_ｂ の方向と、表面内の主屈折率ｎ_ｃ またはｎ_ａ の方向とが時計まわり、または反時計まわりに傾斜することにより、上記屈折率楕円体が傾斜している光学位相差板２・３を備えた構成の液晶表示装置において、液晶の閾値電圧に近い電圧を液晶に印加した中間調表示状態を行うための印加電圧値を、該電圧を印加した状態で反視角方向の階調反転が発生しない範囲に設定した構成である。
【００９５】
これにより、液晶表示素子１に生じる視角に対応する位相差の上記の光学位相差板２・３による補償機能と共に、白階調時の液晶印加電圧を上記の範囲に設定したことによる補償機能により、視角に依存した反視角方向の白階調時（ノーマリホワイト表示であるので）に発生する反転現象を特に効果的に改善することが可能であり、同時に、コントラスト変化も改善して、高品質の画像を表示できる。
【００９６】
さらに、第２の参考例の液晶表示装置でも、液晶層８における液晶材料として、波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）が、０．０６０より大きく０．１２０より小さい範囲に設計されたものを、より好ましくは、上記Δｎ（５５０）が、０．０７０以上０．０９５以下の範囲に設計された液晶材料を用いることで、光学位相差板２・３による位相差の補償機能、及び白階調時の液晶印加電圧を上記の範囲に設定したことによる補償機能に加えて、反視角方向のコントラスト比の低下、左右方向の反転現象をより一層改善することが可能となる。
【００９７】
なお、ここでも、ノーマリホワイト表示の液晶表示装置を例示して説明したが、ノーマリブラック表示の液晶表示装置においても、光学位相差板２・３による補償効果に合わせて、液晶の閾値電圧に近い電圧を液晶に印加して得られる中間調を表示（黒階調）するための液晶印加電圧を、該中間調で反視角方向の階調反転が発生しない範囲に設定し、これによる補償効果を得ることで、上記と同様の効果を得ることができる。
【００９８】
また、前述の第１の参考例の液晶表示装置と同様に、単純マトリクス方式の液晶表示装置以外に、ＴＦＴなどの能動スイッチング素子を用いたアクティブマトリクス方式の液晶表示装置についても適用が可能である。
【００９９】
以下、本発明に係る実施の形態の液晶表示装置について説明する。尚、説明の便宜上、前述した第１及び第２の各参考例にて示した部材と同一の機能を有する部材には、同一の符号を付記し、その説明を省略する。
【０１００】
本実施の形態に係る液晶表示装置（以下、本液晶表示装置）は、前述した図１に示す第１の参考例の液晶表示装置とほぼ同様の構成を有している。異なる点は、第１の参考例の液晶表示装置では、光学位相差板２・３による位相差の補償機能と最良な特性を有する組み合わせとなるように、上記液晶層８のプレティルト角が、液晶層８に液晶の閾値電圧に近い電圧を印加した中間調表示状態で反視角方向の階調反転が発生しない範囲に設定されていたのに対し、本実施の形態の液晶表示装置では、光学位相差板２・３による位相差の補償機能と最良な特性を有する組み合わせとなるように、液晶層８における液晶材料の屈折率異方性Δｎの光の波長に対する変化と、上記光学位相差板の屈折率異方性Δｎの光の波長に対する変化との変化度合を、視角に依存した液晶画面の着色が発生しない範囲に設定している点である。
【０１０１】
以下、この点を詳細に説明する。液晶層８における液晶材料の屈折率異方性Δｎの光の波長に対する変化と、上記光学位相差板の屈折率異方性Δｎの光の波長に対する変化との変化度合を、視角に依存した液晶画面の着色が発生しない範囲に設定することとは、具体的には、以下に示す▲１▼・▲２▼の少なくとも１つの設定範囲の条件を満たすような組み合わせで光学位相差板２・３及び液晶材料を用いれば良い。
【０１０２】
▲１▼ 上記液晶層８における液晶材料の波長４５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （４５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （５５０）の比であるΔｎ_Ｌ （４５０）／Δｎ_Ｌ （５５０）と、光学位相差板２・３の波長４５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （４５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （５５０）の比であるΔｎ_Ｆ （４５０）／Δｎ_Ｆ （５５０）とを、
【０１０３】
【数９】

【０１０４】
の関係を満たすように設定すればよい。そして、より好ましくは、
【０１０５】
【数１０】

【０１０６】
さらに好ましくは、
【０１０７】
【数１１】

【０１０８】
の関係を満たすように設定することである。
【０１０９】
▲２▼ 上記液晶層８における液晶材料の波長６５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （６５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （５５０）の比であるΔｎ_Ｌ （６５０）／Δｎ_Ｌ （５５０）と、光学位相差板２・３の波長６５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （６５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （５５０）の比であるΔｎ_Ｆ （６５０）／Δｎ_Ｆ （５５０）とを、
【０１１０】
【数１２】

【０１１１】
の関係を満たすように設定すればよい。そして、より好ましくは、
【０１１２】
【数１３】

【０１１３】
さらに好ましくは、
【０１１４】
【数１４】

【０１１５】
の関係を満たすように設定することである。
【０１１６】
このような▲１▼・▲２▼の少なくとも何れか一方を満たすように設計された液晶材料と光学位相差板とを用いることで、光学位相差板２・３による位相差の補償機能による表示画面の視角に依存して生ずるコントラスト変化、反転現象、着色現象の改善のみならず、表示画面の着色現象を特に効果的に改善できる。
【０１１７】
詳しく述べると、▲１▼・▲２▼の広い方の範囲を少なくとも一方満たすことで、通常の液晶表示装置にて要求される視角５０°において、若干の色付きはあるものの、どの方向から見ても充分に使用に耐えうるものとできる。また、上記▲１▼・▲２▼におけるより好ましいとした範囲を少なくとも一方満たすことで、視角６０°で若干の色付きはあるものの、どの方向から見ても充分に使用に耐えうるものとできる。そして、特に上記▲１▼・▲２▼におけるさらに好ましいとした範囲を少なくとも一方満たすことで、どの方向から見ても着色の一切ないものとできる。
【０１１８】
また、▲１▼・▲２▼の少なくとも１つを満たすことで、コントラスト変化、反転現象についても、光学位相差板２・３の補償機能のみの場合よりも改善が図れる。
【０１１９】
図１０に、本液晶表示装置における液晶層８に用いることのできる液晶材料と、光学位相差板２・３に用いることのできる光学位相差板の一組み合わせにおける、それぞれの波長（λ）に対するΔｎ（λ）／Δｎ（５５０）を示す。実線にて示す曲線ａが、一液晶材料の波長（λ）に対するΔｎ（λ）／Δｎ（５５０）であり、一点鎖線にて示す曲線ｂが、一光学位相差板の波長（λ）に対するΔｎ（λ）／Δｎ（５５０）である。
【０１２０】
以上のように、本実施の形態の液晶表示装置は、液晶表示素子１と偏光板４・５の間に、屈折率楕円体の３つの主屈折率ｎ_ａ 、ｎ_ｂ 、ｎ_ｃ がｎ_ａ ＝ｎ_ｃ ＞ｎ_ｂ という関係を有し、表面内の主屈折率ｎ_ａ またはｎ_ｃ の方向を軸として、表面の法線方向に平行な主屈折率ｎ_ｂ の方向と、表面内の主屈折率ｎ_ｃ またはｎ_ａ の方向とが時計まわり、または反時計まわりに傾斜することにより、上記屈折率楕円体が傾斜している光学位相差板２・３を備えた構成の液晶表示装置において、液晶層８における液晶材料の屈折率異方性Δｎの光の波長に対する変化と、上記光学位相差板の屈折率異方性Δｎの光の波長に対する変化との変化度合を、視角に依存した液晶画面の着色が発生しない範囲に設定した構成である。
【０１２１】
これにより、液晶表示素子１に生じる視角に対応する位相差の上記の光学位相差板２・３による補償機能と共に、液晶層８における液晶材料の屈折率異方性Δｎの光の波長に対する変化と、上記光学位相差板の屈折率異方性Δｎの光の波長に対する変化との変化度合を上記の範囲に設定したことによる補償機能により、視角に依存した表示画面の着色を特に効果的に改善することが可能で、同時に、コントラスト変化、階調反転も改善して、高品質の画像を表示できる。
【０１２２】
さらに、本実施の形態の液晶表示装置でも、液晶層８における液晶材料として、波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）が、０．０６０より大きく０．１２０より小さい範囲に設計されたものを、より好ましくは、上記Δｎ（５５０）が、０．０７０以上０．０９５以下の範囲に設計された液晶材料を用いることで、光学位相差板２・３による位相差の補償機能、及び上記の変化度合を上記の範囲に設定したことによる補償機能に加えて、反視角方向のコントラスト比の低下、左右方向の反転現象をより一層改善することが可能となる。
【０１２３】
なお、ここでも、ノーマリホワイト表示の液晶表示装置を例示して説明したが、ノーマリブラック表示の液晶表示装置においても、上記と同様の効果を得ることができる。
【０１２４】
また、前述の参考例１の液晶表示装置と同様に、単純マトリクス方式の液晶表示装置以外に、ＴＦＴなどの能動スイッチング素子を用いたアクティブマトリクス方式の液晶表示装置についても適用が可能である。
【０１２５】
【実施例】
次に、本発明の実施の形態に係る液晶表示装置の効果を裏付ける実施例を説明する。
【０１２６】
（参考例１）
本参考例は、上記の第１の参考例及び第２の参考例に係る液晶表示装置の効果を裏付けるためのものであり、ここでは、図１の液晶表示装置における液晶セル１６の配向膜１１・１４に、日本合成ゴム社製のオプトマーＡＬ（商品名）を用い、上記配向膜１１・１４に対してプレティルト角が、２．０°，３．０°，４．０°，５．０°，１０．０°，１１．０°，１２．０°となる液晶材料を用い、セル厚（液晶層８の厚み）を５μｍとした、５つのサンプルセル♯１〜♯７を用意した。
【０１２７】
これらサンプルセル♯１〜♯７のプレティルト角の測定は、サンプルセル♯１〜♯７の材料を注入したホモジニアスセルを作成し、プレティルト角測定装置ＮＳＭＡＰ−３０００ＬＣＤ（シグマ光機社製）で測定した。
【０１２８】
また、サンプルセル♯１〜♯７における光学位相差板２・３としては、透明な支持体（例えば、トリアセチルセルロース（ＴＡＣ）等）にディスコティック液晶を塗布し、ディスコティック液晶を傾斜配向させて架橋して形成してなる、上述の第１のリタデーション値が０ｎｍ、上述の第２のリタデーション値が１００ｎｍであり、主屈折率ｎ_ｂ の方向がｘｙｚ軸座標におけるｚ軸方向に対して矢印Ａで示す方向に約２０°となるように傾いており、同様に主屈折率ｎ_ｃ の方向がｘ軸に対して矢印Ｂで示す方向に約２０°の角度をなしているもの（即ち、屈折率楕円体の傾斜角度θ＝２０°のもの）を用いた。
【０１２９】
これらサンプルセル♯１〜♯７に対して、白階調時の印加電圧を種々変えて、白色光のもと目視試験を行った結果を表１〜表７に示す。
【０１３０】
【表１】

【０１３１】
表１は、白階調を得るための液晶印加電圧として、液晶への印加電圧がゼロのオフ状態における、液晶セル１６の表面の法線方向の透過率を１００％としてその１００％の透過率を法線方向において得る値を個々のサンプルセル毎に設定し、白階調時の表示状態を調べた結果である。
【０１３２】
表１より、透過率を１００％として白階調時の電圧を設定した場合、プレティルト角を５．０°，１０．０°としたサンプルセル♯４，♯５では、視角を７０°として反視角方向から見ても階調反転は確認されず良好な画質であった。
【０１３３】
また、プレティルト角を３．０°としたサンプルセル♯２、プレティルト角を４．０°としたサンプルセル♯３では、何れも視角６０°までは反視角方向から見ても階調反転は確認されず良好な画質であったが、視角７０°とすると、サンプルセル♯２では、使用に耐えうる程度の階調反転が確認され、サンプルセル♯３では階調反転は無いものの、階調がつぶれた。しかしながら、何れも、視角７０°で充分に使用に耐え得るものであった。
【０１３４】
プレティルト角を１１．０°としたサンプルセル♯６では、視角６０°までは良好な画質であったが、視角７０°で正視角方向から見た場合に使用に耐えない程輝度が低下することが確認された。
【０１３５】
一方、プレティルト角を２．０°としたサンプルセル♯１では、視角５０°においてでさえ反視角方向から見た場合に、階調反転が確認され、また、プレティルト角を１２．０°としたサンプルセル♯７では、視角５０°においてでさえ正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１３６】
【表２】

【０１３７】
表２は、オフ状態の透過率に対する透過率を９７％として白階調時の電圧を個々のサンプルセル毎に設定して調べた結果である。
【０１３８】
表２より、透過率を９７％として白階調時の電圧を設定した場合、プレティルト角を４．０°，５．０°，１０．０°としたサンプルセル♯３，♯４，♯５では、視角を７０°として反視角方向から見ても階調反転は確認されず良好な画質であった。
【０１３９】
プレティルト角を３．０°としたサンプルセル♯２では、視角５０°までは反視角方向から見ても階調反転は確認されず良好な画質であったが、視角６０°で階調がつぶれた。しかしながら、階調反転は確認されなかったので、視角６０°でも使用に耐え得るものであった。プレティルト角を１１．０°としたサンプルセル♯６では、視角５０°までは良好な画質であったが、視角６０°で正視角方向から見た場合に、使用に耐えない程輝度が低下することが確認された。
【０１４０】
一方、プレティルト角を２．０°としたサンプルセル♯１では、視角５０°においてでさえ反視角方向から見た場合に階調反転が確認された。また、プレティルト角を１２．０°としたサンプルセル♯７では、視角５０°においてでさえ正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１４１】
【表３】

【０１４２】
表３は、オフ状態の透過率に対する透過率を９５％として白階調時の電圧を個々のサンプルセル毎に設定して調べた結果である。これは、透過率を９５％として電圧設定を行った表２と同じ結果であった。
【０１４３】
【表４】

【０１４４】
表４は、オフ状態の透過率に対する透過率を９２％として白階調時の電圧を個々のサンプルセル毎に設定して調べた結果である。
【０１４５】
表４より、透過率を９２％として白階調時の電圧を設定した場合、プレティルト角を４．０°，５．０°，１０．０°としたサンプルセル♯３，♯４，♯５では、視角を７０°として反視角方向から見ても階調反転は確認されず良好な画質であった。
【０１４６】
プレティルト角を３．０°としたサンプルセル♯２では、視角６０°までは反視角方向から見ても階調反転は確認されず良好な画質であったが、視角７０°で階調が反転した。しかしながら、使用に耐え得る程度のものであった。プレティルト角を１１．０°としたサンプルセル♯６では、視角５０°までは良好な画質であったが、視角６０°で正視角方向から見た場合に使用に耐えない程輝度が低下することが確認された。プレティルト角を２．０°としたサンプルセル♯１では、視角５０°で階調が反転したが、使用に耐え得る程度のものであった。
【０１４７】
一方、プレティルト角を１２．０°としたサンプルセル♯７では、視角５０°においてでさえ正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１４８】
【表５】

【０１４９】
表５は、オフ状態の透過率に対する透過率を９０％として白階調時の電圧を個々のサンプルセル毎に設定して調べた結果である。
【０１５０】
表５より、透過率を９０％として白階調時の電圧を設定した場合、プレティルト角を４．０°，５．０°としたサンプルセル♯３，♯４では、視角を７０°として反視角方向から見ても階調反転は確認されず良好な画質であった。
【０１５１】
プレティルト角を１０．０°としたサンプルセル♯５では、視角５０°までは良好な画質であったが、視角６０°で正視角方向から見た場合に輝度が低下することが確認された。しかしながら、この輝度低下は使用に耐え得る程度のものであった。プレティルト角を３．０°としたサンプルセル♯２では、視角６０°までは反視角方向から見ても階調反転は確認されず良好な画質であったが、視角７０°で階調がつぶれた。しかしながら、階調反転は無く、使用に耐え得る程度のものであった。プレティルト角を１１．０°としたサンプルセル♯６では、視角５０°で正視角方向から見た場合に輝度が低下することが確認されたが、この輝度低下は使用に耐え得る程度のものであった。プレティルト角を２．０°としたサンプルセル♯１では、視角５０°で階調がつぶれ、視角６０で階調が反転したが、使用に耐え得る程度のものであった。
【０１５２】
一方、プレティルト角を１２．０°としたサンプルセル♯７では、視角５０°においてでさえ正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１５３】
【表６】

【０１５４】
表６は、オフ状態の透過率に対する透過率を８７％として白階調時の電圧を個々のサンプルセル毎に設定して調べた結果である。
【０１５５】
表６より、透過率を８７％として白階調時の電圧を設定した場合、プレティルト角を３．０°，４．０°，５．０°としたサンプルセル♯２，♯３，♯４では、視角５０°までは良好な画質であったが、視角６０°で正視角方向から見た場合に輝度が低下することが確認された。しかしながら、この輝度低下は使用に耐え得る程度のものであった。なお、視角７０°では、正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１５６】
プレティルト角を１０．０°としたサンプルセル♯５では、視角５０°、視角６０°で正視角方向から見た場合に輝度が低下することが確認されたが、使用に耐え得る程度のものであった。なお、視角７０°では、正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１５７】
プレティルト角を１１．０°，１２．０°としたサンプルセル♯６，♯７では、視角５０°においてでさえ、正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１５８】
プレティルト角を２．０としたサンプルセル♯１では、視角５０°までは反視角方向から見ても階調反転は確認されず良好な画質であったが、視角６０°で正視角方向から見た場合に輝度低下が確認された。しかしながら、使用に耐え得る程度のものであった。なお、視角７０°では、正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１５９】
【表７】

【０１６０】
表７は、オフ状態の透過率に対する透過率を８５％として白階調時の電圧を個々のサンプルセル毎に設定して調べた結果である。
【０１６１】
表７より、透過率を８５％として白階調時の電圧を設定した場合、プレティルト角を３．０°，４．０°，５．０°，１０．０°，１１．０°，１２．０°としたサンプルセル♯２，♯３，♯４，♯５，♯６，♯７では、視角５０°においてでさえ正視角方向、左右方向から見た場合に、使用に耐えない程の輝度低下が確認された。
【０１６２】
一方、プレティルト角を２．０としたサンプルセル♯１では、視角５０°で正視角方向から見た場合に輝度低下が確認されたが、使用に耐え得るものであった。なお、視角６０°では、正視角方向から見た場合に使用に耐えない程の輝度低下が確認された。
【０１６３】
即ち、表１〜表７より、プレティルト角を調整すること、或いは、白階調時の透過率を調整することで、反視角方向の階調反転を改善できると言える。その場合、白階調の透過率として通常設定される９５〜９７％程度では、プレティルト角を２°より大きく１２°未満の範囲とすることで、視角５０°において反視角方向の階調反転を改善し、かつ、正視角方向の輝度低下もない良好な表示とできると言える。そして、さらに、４°以上１０°以下の範囲とすることで、広視野角の視角７０°においても反視角方向の階調反転を改善し、かつ、正視角方向の輝度低下もない良好な表示とできると言える。
【０１６４】
また、通常設定される２°〜１０°のプレティルト角では、白階調時の透過率として８５％より大きい透過率を得るようにすることで、視角５０°において反視角方向の階調反転を改善し、かつ、正視角方向の輝度低下もない良好な表示とできると言える。そして、さらに、９０％以上９７％以下の範囲に入る透過率を得るようにすることで、プレティルト角を調整することで、広視野角の視角７０°においても反視角方向の階調反転を改善し、かつ、正視角方向の輝度低下もない良好な表示とできると言える。
【０１６５】
また、プレティルト角の調整と白階調時の透過率の調整とを組み合わせることで、さらに、改善の効果が得られると言える。
【０１６６】
次に、上記と同じサンプルセル♯１とサンプルセル♯４に対して、図６に示すように、受光素子２１、増幅器２２および記録装置２３を備えた測定系を用いて、液晶表示装置の視角依存性を調べた。
【０１６７】
この測定系において、液晶表示装置の液晶セル１６は、前記のガラス基板９側の面１６ａが直交座標ＸＹＺの基準面Ｘ−Ｙに位置するように設置される。受光素子２１は、一定の立体受光角で受光し得る素子であり、面１６ａに垂直なＺ方向に対して角度φ（視角）をなす方向における、座標原点から所定距離をおいた位置に配置されている。
【０１６８】
測定時には、本測定系に設置された液晶セル１６に対し、面１６ａの反対側の面から波長５５０ｎｍの単色光を照射する。液晶セル１６を透過した単色光の一部は、受光素子２１に入射する。受光素子２１の出力は、増幅器２２で所定のレベルに増幅された後、波形メモリ、レコーダなどの記録装置２３によって記録される。
【０１６９】
ここでは、受光素子２１が一定の角度φで固定された場合の、上記のサンプルセル♯１，♯４への印加電圧に対する受光素子２１の出力レベルを測定した。
【０１７０】
測定は、５０°の角度φとなるように受光素子２１を配置し、Ｙ方向が画面の左側であり、Ｘ方向が画面の下側（正視角方向）であると仮定して、受光素子２１の配置位置を上方向（反視角方向）、下方向（正視角方向）、左右方向にそれぞれ変えて行われた。
【０１７１】
その結果を、図７（ａ）〜（ｃ）に示す。図７（ａ）〜（ｃ）は、プレティルト角を５．０°としたサンプルセル♯４及びプレティルト角を２．０°としたサンプルセル♯１に印加される電圧に対する光の透過率（透過率−液晶印加電圧特性）を表したグラフである。
【０１７２】
図７（ａ）が図２の上方向から測定を行った結果であり、図７（ｂ）が図２の下方向、図７（ｃ）が左右方向から測定をそれぞれ行った結果である。
【０１７３】
図７（ａ）において、一点鎖線で示す曲線Ｌ１は、正面、即ち表面の法線方向から測定した結果であり、サンプルセル♯１，♯４とも、同じ透過率−液晶印加電圧特性となる。
【０１７４】
図７（ａ）〜（ｃ）において、実線で表すＬ２・Ｌ４・Ｌ６が、サンプルセル♯４のもので、破線で示す曲線Ｌ３・Ｌ５・Ｌ７が、サンプルセル♯１のものである。
【０１７５】
サンプルセル♯４及びサンプルセル♯１について、上方向の透過率−液晶印加電圧特性を比較した場合、図７（ａ）より、サンプルセル♯１の曲線Ｌ３は、１Ｖ付近から２Ｖ付近に欠けて透過率が一度上がってから下がり、こぶを持っているのに対し、サンプルセル♯４の曲線Ｌ２は、１Ｖ付近から２Ｖ付近に欠けて透過率がほぼ一定であり、こぶが消滅し、反転現象が無いことが確認された。
【０１７６】
また、図７（ｂ）（ｃ）にて、下方向及び左右方向の透過率−液晶印加電圧特性を比較すると、サンプルセル♯４の曲線Ｌ４・Ｌ６はそれぞれサンプルセル♯１の曲線Ｌ５・Ｌ７に対して少し速く透過率が落ちはじめることを示しているが、図７（ｂ）では２．５Ｖ付近、図７（ｃ）では３Ｖ付近から、サンプルセル♯４の透過率はサンプルセル♯１のものにほぼ一致しており、プレティルト角を５．０°と大きくしたことによる悪影響はないことが確認できる。
【０１７７】
また、光学位相差板２・３として、透明な支持体にディスコティック液晶をハイブリッド配向させた以外は、上記のサンプルセル♯１〜♯７と同様のサンプルセルに対しても、上記と同様の結果が得られた。
【０１７８】
（実施例１）
本実施例は、上記の第１及び第２の各参考例、及び実施の形態に係る液晶表示装置の効果を裏付けるためのものであり、ここでは、図１の液晶表示装置における液晶セル１６の配向膜１１・１４に、日本合成ゴム社製のオプトマーＡＬ（商品名）を用い、上記配向膜１１・１４に対してプレティルト角が３°で、かつ波長５５０ｎｍにおける屈折率異方性Δｎ（５５０）がそれぞれ、０．０７０、０．０８０、０．０９５に設定された液晶材料を液晶層８に用い、セル厚（液晶層８の厚み）を５μｍとした、３つのサンプルセル♯１６〜♯１８を用意した。
【０１７９】
ここでも、プレティルト角は、サンプルセル♯１６〜♯１８の材料を注入したホモジニアスセルを作成し、プレティルト角測定装置ＮＳＭＡＰ−３０００にて測定した。
【０１８０】
また、これらサンプルセル♯１６〜♯１８における光学位相差板２・３としては、ディスコティック液晶を傾斜配向した前述の比較例１における光学位相差板２・３と同様のものを用いた。
【０１８１】
そして、前述の参考例１で説明したと同様の図６に示す測定系を用いて、受光素子２１が一定の角度φで固定された場合の、サンプルセル♯１６〜♯１８への印加電圧に対する受光素子２１の出力レベルを測定した。
【０１８２】
測定は、参考例１と同様に、５０°の角度φとなるように受光素子２１を配置し、Ｙ方向が画面の左側であり、Ｘ方向が画面の下側（正視角方向）であると仮定して、受光素子２１の配置位置を上方向（反視角方向）、下方向（正視角方向）、左右方向にそれぞれ変えて行われた。
【０１８３】
その結果を、図８（ａ）〜（ｃ）に示す。図８（ａ）〜（ｃ）は、サンプルセル♯１６〜♯１８に印加される電圧に対する光の透過率（透過率−液晶印加電圧特性）を表したグラフである。
【０１８４】
図８（ａ）が図２の上方向から測定を行った結果であり、図８（ｂ）が図２の右方向、図８（ｃ）が左方向から測定をそれぞれ行った結果である。
【０１８５】
図８（ａ）〜（ｃ）において、それぞれ一点鎖線で示す曲線Ｌ８・Ｌ１１・Ｌ４が、液晶層８にΔｎ（５５０）＝０．０７０の液晶材料を用いたサンプルセル♯１６のもので、実線で示す曲線Ｌ９・Ｌ１２・Ｌ１５が、液晶層８にΔｎ（５５０）＝０．０８０の液晶材料を用いたサンプルセル♯１７のもので、破線で示す曲線Ｌ１０・Ｌ１３・Ｌ１６が、液晶層８にΔｎ（５５０）＝０．０９５の液晶材料を用いたサンプルセル♯１８のものである。
【０１８６】
また、本実施例に対する比較例として、図１の液晶セル１６における液晶層８に波長５５０ｎｍにおける屈折率異方性Δｎ（５５０）がそれぞれ、０．０６０、０．１２０に設定された液晶材料を用いた以外は本実施例と同様の２つの比較用サンプルセル♯１０３，♯１０４を用意し、図６に示す測定系に設置して、本実施例と同様の方法で受光素子２１が一定の角度φで固定された場合の比較用サンプルセル♯１０３，♯１０４への印加電圧に対する受光素子２１の出力レベルも測定した。
【０１８７】
測定は、本実施例と同様に、５０°の角度φとなるように受光素子２１を配置し、Ｙ方向が画面の左側であり、Ｘ方向が画面の下側（正視角方向）であると仮定して、受光素子２１の配置位置を上方向（反視角方向）、右方向、左方向にそれぞれ変えて行われた。
【０１８８】
その結果を、図９（ａ）〜（ｃ）に示す。図９（ａ）〜（ｃ）は、比較例サンプル♯１０３，♯１０４に印加される電圧に対する光の透過率（透過率−液晶印加電圧特性）を表したグラフである。
【０１８９】
図９（ａ）が図２の上方向から測定を行った結果であり、図９（ｂ）が図２の右方向、図９（ｃ）が左方向からの測定をそれぞれ行った結果である。
【０１９０】
図９（ａ）〜（ｃ）において、実線で示す曲線Ｌ１７・Ｌ１９・Ｌ２１が、液晶層８にΔｎ（５５０）＝０．０６０の液晶材料を用いた比較用サンプルセル♯１０３のもので、破線で示す曲線Ｌ１８・Ｌ２０・Ｌ２２が、液晶層８にΔｎ（５５０）が０．１２０の液晶材料を用いた比較用サンプルセル♯１０４のものである。
【０１９１】
サンプルセル♯１６〜♯１８と、比較用サンプルセル♯１０３，♯１０４とについて、上方向の透過率−液晶印加電圧特性を比較した場合、図８（ａ）では、曲線Ｌ９・Ｌ８・Ｌ１０とも電圧を高くするに伴って透過率が充分下がることが確認された。これに対して、図９（ａ）では、曲線Ｌ１８は、図８（ａ）の曲線Ｌ８・Ｌ９・Ｌ１０と比較して、電圧を高くしていっても充分に透過率が下がっていない。また、曲線Ｌ１７は、電圧を高くしていくに伴い透過率は一度低下してから再び上昇する反転現象が確認された。
【０１９２】
同様に、サンプルセル♯１６〜♯１８と比較用サンプルセル♯１０３，♯１０４とについて、右方向の透過率−液晶印加電圧特性を比較した場合、図８（ｂ）では、曲線Ｌ１１・Ｌ１２・Ｌ１３とも電圧を高くしていくと透過率はほぼ０近くになるまで低下していることが確認された。また、図９（ｂ）でも、曲線Ｌ１９は電圧を高くしていくと、図８（ｂ）と同様に透過率がほぼ０近くになるまで低下するが、曲線Ｌ２０については上記の反転現象が確認された。
【０１９３】
同様に、サンプルセル♯１６〜♯１８と比較用サンプルセル♯１０３，♯１０４とについて、左方向の場合でも右方向と同様のことが確認された。
【０１９４】
さらに、サンプルセル♯１６〜♯１８と比較用サンプルセル♯１０３，♯１０４とについて、白色光のもとで目視確認を行った。
【０１９５】
サンプルセル♯１６〜♯１８及び比較用サンプルセル♯１０３については、視角を５０°としてどの方向から見ても、着色は確認されず良好な画質であった。これに対し、比較用サンプルセル♯１０４については、視角を５０°として左右方向から見た場合に、黄色から橙色に着色していることが確認された。
【０１９６】
以上の結果から、図８（ａ）〜（ｃ）で示したように、液晶層８に波長５５０ｎｍにおける屈折率異方性Δｎ（５５０）がそれぞれ、０．０７０、０．０８０、０．０９５に設定された液晶材料を用いた場合には、電圧を印加していくと透過率は充分低下し、反転現象も見られないため、視野角が拡大し、また、着色現象もなく、液晶表示装置の表示品位が格段に向上していることがわかる。
【０１９７】
それに対して、図９（ａ）〜（ｃ）で示したように、液晶層８に波長５５０ｎｍにおける屈折率異方性Δｎ（５５０）がそれぞれ、０．０６０、０．１２０に設定された液晶材料を用いた場合には、視角依存性は充分に改善されないことがわかる。
【０１９８】
また、光学位相差板２・３として、透明な支持体にディスコティック液晶をハイブリッド配向させた以外は、上記のサンプルセル♯１６〜♯１８、及び比較用サンプルセル♯１０３，♯１０４と同様の、サンプルセル、比較用サンプルセルに対しても、同様の結果が得られた。
【０１９９】
また、上記光学位相差板２・３の屈折率楕円体の傾斜角度θを変化させて、傾斜角度θに対する透過率−液晶印加電圧特性の依存性を調べた結果、１５°≦θ≦７５°の範囲内であれば、光学位相差板２・３におけるディスコティック液晶の配向の状態に関係なく、基本的に変化しなかった。尚、上記範囲を越えた場合には、反視角方向の視野角が広がらないことが確認された。
【０２００】
さらに、上記光学位相差板２・３の第２のリタデーション値を変化させて、第２のリタデーション値に対する透過率−液晶印加電圧特性の依存性を調べた結果、第２のリタデーション値が８０ｎｍ〜２５０ｎｍの範囲内であれば、位相差板２・３におけるディスコティック液晶の配向の状態に関係なく、基本的に変化しなかった。尚、上記範囲を越えた場合には、左右方向の視野角が広がらないことが確認された。
【０２０１】
また、上記比較用サンプルセル♯１０３，♯１０４の目視試験の結果を基に、図１の液晶セル１６における液晶層８に波長５５０ｎｍにおける屈折率異方性Δｎ（５５０）がそれぞれ、０．０６５、０．１００、０．１１５の液晶材料を用いた以外は本実施例と同様の３つのサンプルセル♯１９〜♯２１を用意し、図６に示した測定系を用いて、本実施例と同様の方法で受光素子２１が一定の角度φで固定された場合のサンプルセル♯１９〜♯２１への印加電圧に対する受光素子２１の出力レベルを測定した。また、それぞれ白色光のもとで目視確認を行った。
【０２０２】
その結果、屈折率異方性Δｎ（５５０）を０．１００としたサンプルセル♯２０、及び屈折率異方性Δｎ（５５０）を０．１１５としたサンプルセル♯２１では、角度φ５０°とした場合、左右方向において電圧を高くするとわずかに透過率の上昇が確認された。しかしながら、目視においては反転現象は生じておらず、この程度の透過率の上昇は使用に耐えうるものであった。上方向の結果においては何ら問題なかった。一方、屈折率異方性Δｎ（５５０）を０．０６５としたサンプルセル♯１９では、前述した比較用サンプルセル♯１０３と同様に、上方向において電圧を高くすると透過率は一度沈んで浮き上がるような曲線となったが、図９（ａ）に示した比較用サンプルセル♯１０３のものに比べて透過率の上昇の度合は小さく、使用に耐えうるものであった。左右方向の結果においては何ら問題なかった。
【０２０３】
また、目視検査においては、サンプルセル♯２０，♯２１では、黄色から橙色の若干の着色が確認されたが、問題にならない程度であった。サンプルセル♯１９では、若干ではあるが青みを呈していることが確認された。しかしながら、この程度の青みも問題にならないものであった。
【０２０４】
また、補足として、サンプルセル♯１９と比較用サンプルセル♯１０３とについて、１Ｖ程度の電圧を印加し、液晶セル１６の表面の法線方向の白表示時の透過率を測定した。その結果、比較用サンプルセル♯１０３では、使用に耐えない程度の透過率の低下が見られた。これに対し、サンプルセル♯１９では、若干の透過率の低下が確認されたが、使用に耐えうる程度のものであった。
【０２０５】
さらに、図１の液晶表示装置における液晶セル１６の配向膜１１・１４に日本合成ゴム社製のオプトマーＡＬ（商品名）を用い、上記配向膜１１・１４に対してプレティルト角が４°，５°，１０°，１１°となる液晶材料を液晶層８にそれぞれ用いた場合においても同様の結果が得られた。
【０２０６】
（実施例２）
本実施例は、上記の実施の形態に係る液晶表示装置の効果を裏付けるためのものであり、ここでは、図１の液晶表示装置における液晶セル１６の液晶層８に、波長４５０ｎｍにおける屈折率異方性Δｎ_Ｌ （４５０）と波長５５０ｎｍにおける屈折率異方性Δｎ_Ｌ （５５０）と、光学位相差板２・３の波長４５０ｎｍにおける屈折率異方性Δｎ_Ｆ （４５０）と波長５５０ｎｍにおける屈折率異方性Δｎ_Ｆ （５５０）との式（１）にて表される関係が、それぞれ、０，０．１５，０．２５，０．３０，０．３３に設定された液晶材料と光学位相差板を用い、セル厚（液晶層８の厚み）を５μｍとした、５つのサンプルセル♯３１〜♯３５を用意した。
【０２０７】
【数１５】

【０２０８】
サンプルセル♯３１〜♯３５における光学位相差板２・３としては、透明な支持体（例えば、トリアセチルセルロース（ＴＡＣ）等）にディスコティック液晶を塗布し、ディスコティック液晶を傾斜配向させて架橋して形成してなる、上述の第１のリタデーション値が０ｎｍ、上述の第２のリタデーション値が１００ｎｍであり、主屈折率ｎ_ｂ の方向がｘｙｚ軸座標におけるｚ軸方向に対して矢印Ａで示す方向に約２０°となるように傾いており、同様に主屈折率ｎ_ｃ の方向がｘ軸に対して矢印Ｂで示す方向に約２０°の角度をなしているもの（即ち、屈折率楕円体の傾斜角度θ＝２０°のもの）を用いた。
【０２０９】
また、本実施例に対する比較例として、図１の液晶表示装置における液晶セル１６の液晶層８に、上記の式（１）にて表される関係が、０．３５，１．０，１．１の液晶材料、光学位相差板を用いた以外は本実施例と同様の比較用サンプルセル♯３０１〜♯３０３を用意した。
【０２１０】
上記のサンプルセル♯３１〜♯３５及び比較用サンプルセル♯３０１〜♯３０３について、白色光のもと目視試験を行った結果を表８に示す。
【０２１１】
【表８】

【０２１２】
サンプルセル♯３１〜♯３３については、視角を７０°としてどの方向から見ても着色は確認されず良好な画質であった。サンプルセル♯２４では、視角５０°まではどの方向から見ても着色は確認されず良好な画質であったが、視角６０°では、左右方向から見た場合に若干の着色が確認されたが、使用に耐えうる程度の着色であった。サンプルセル♯２５では、視角５０°まではどの方向から見ても着色は確認されず良好な画質であったが、視角６０°では、左右方向から見た場合に使用に耐えない程度の着色が確認された。
【０２１３】
これに対し、比較用サンプルセル♯３０１〜♯３０３では、視角５０°においてでさえ左右方向から見た場合に、使用に耐えない程の黄色から橙色の着色が確認された。
【０２１４】
また、光学位相差板２・３として、透明な支持体にディスコティック液晶をハイブリッド配向させた以外は、本実施例のサンプルセル♯３１〜♯３５、比較用サンプルセル♯３０１〜♯３０３と同様のサンプルセル、比較用サンプルセルについても、上記と同様の結果が得られた。
【０２１５】
（実施例３）
本実施例は、上記の実施の形態３に係る液晶表示装置の効果を裏付けるためのものであり、ここでは、図１の液晶表示装置における液晶セル１６の液晶層８に、波長５５０ｎｍにおける屈折率異方性Δｎ_Ｌ （５５０）と波長６５０ｎｍにおける屈折率異方性Δｎ_Ｌ （６５０）と、光学位相差板２・３の波長５５０ｎｍにおける屈折率異方性Δｎ_Ｆ （５５０）と波長６５０ｎｍにおける屈折率異方性Δｎ_Ｆ （６５０）との式（２）にて表される関係が、それぞれ、０，０．１０，０．２０，０．２３，０．２５に設定された液晶材料と光学位相差板を用い、セル厚（液晶層８の厚み）を５μｍとした、５つのサンプルセル♯４１〜♯４５を用意した。
【０２１６】
【数１６】

【０２１７】
サンプルセル♯４１〜♯４５における光学位相差板２・３としては、透明な支持体（例えば、トリアセチルセルロース（ＴＡＣ）等）にディスコティック液晶を塗布し、ディスコティック液晶を傾斜配向させて架橋して形成してなる、上述の第１のリタデーション値が０ｎｍ、上述の第２のリタデーション値が１００ｎｍであり、主屈折率ｎ_ｂ の方向がｘｙｚ軸座標におけるｚ軸方向に対して矢印Ａで示す方向に約２０°となるように傾いており、同様に主屈折率ｎ_ｃ の方向がｘ軸に対して矢印Ｂで示す方向に約２０°の角度をなしているもの（即ち、屈折率楕円体の傾斜角度θ＝２０°のもの）を用いた。
【０２１８】
また、本実施例に対する比較例として、図１の液晶表示装置における液晶セル１６の液晶層８に、上記の式（２）にて表される関係が、０．２７，１．０、１．１の液晶材料、光学位相差板を用いた以外は本実施例と同様の比較用サンプルセル♯４０１〜♯４０３を用意した。
【０２１９】
上記のサンプルセル♯４１〜♯４５及び比較用サンプルセル♯４０１〜♯４０３について、白色光のもと目視試験を行った結果を表９に示す。
【０２２０】
【表９】

【０２２１】
サンプルセル♯４１〜♯４３については、視角を７０°としてどの方向から見ても着色は確認されず良好な画質であった。サンプルセル♯４４では、視角５０°まではどの方向から見ても着色は確認されず良好な画質であったが、視角６０°では、左右方向から見た場合に若干の着色が確認されたが、使用に耐えうる程度の着色であった。サンプルセル♯４５では、視角５０°で、左右方向から見た場合に若干の着色が確認されたが、使用に耐えうる程度の着色であった。
【０２２２】
これに対し、比較用サンプルセル♯４０１〜♯４０３では、視角５０°においてでさえ左右方向から見た場合に、使用に耐えない程の黄色から橙色の着色が確認された。
【０２２３】
また、光学位相差板２・３として、透明な支持体にディスコティック液晶をハイブリッド配向させた以外は、本実施例のサンプルセル♯４１〜♯４５、比較用サンプルセル♯４０１〜♯４０３と同様のサンプルセル、比較用サンプルセルについても、上記と同様の結果が得られた。
【０２２４】
【発明の効果】
以上のように、本発明に係る第１の液晶表示装置は、対向する表面に透明電極層及び配向膜がそれぞれ形成された一対の透光性基板の間にほぼ９０°捻じれ配向した液晶層が封入されてなる液晶表示素子と、上記液晶表示素子の両側に配置される一対の偏光子と、上記液晶表示素子と上記偏光子との間に少なくとも１枚介在された光学位相差板であって、屈折率楕円体の３つの主屈折率ｎ_ａ 、ｎ_ｂ 、ｎ_ｃ がｎ_ａ ＝ｎ_ｃ ＞ｎ_ｂ という関係を有し、表面内の主屈折率ｎ_ａ またはｎ_ｃ の方向を軸として、表面の法線方向に平行な主屈折率ｎ_ｂ の方向と、表面内の主屈折率ｎ_ｃ またはｎ_ａ の方向とが時計まわり、または反時計まわりに傾斜することにより、上記屈折率楕円体が傾斜している光学位相差板とを備え、かつ、上記液晶層における液晶材料の、波長４５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （４５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （５５０）の比であるΔｎ_Ｌ （４５０）／Δｎ_Ｌ （５５０）と、上記光学位相差板の波長４５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （４５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （５５０）の比であるΔｎ_Ｆ （４５０）／Δｎ_Ｆ （５５０）とが、
【０２２５】
【数１７】

【０２２６】
の関係を満たすように設定されていることを特徴としている。
【０２２７】
また、より好ましい構成としては、
【０２２８】
【数１８】

【０２２９】
の関係を満たすように設定されていることを特徴としている。
【０２３０】
本発明に係る第２の液晶表示装置は、対向する表面に透明電極層及び配向膜がそれぞれ形成された一対の透光性基板の間にほぼ９０°捻じれ配向した液晶層が封入されてなる液晶表示素子と、上記液晶表示素子の両側に配置される一対の偏光子と、上記液晶表示素子と上記偏光子との間に少なくとも１枚介在された光学位相差板であって、屈折率楕円体の３つの主屈折率ｎ_ａ 、ｎ_ｂ 、ｎ_ｃ がｎ_ａ ＝ｎ_ｃ ＞ｎ_ｂ という関係を有し、表面内の主屈折率ｎ_ａ またはｎ_ｃ の方向を軸として、表面の法線方向に平行な主屈折率ｎ_ｂ の方向と、表面内の主屈折率ｎ_ｃ またはｎ_ａ の方向とが時計まわり、または反時計まわりに傾斜することにより、上記屈折率楕円体が傾斜している光学位相差板とを備え、かつ、上記液晶層における液晶材料の、波長６５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （６５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｌ （５５０）の比であるΔｎ_Ｌ （６５０）／Δｎ_Ｌ （５５０）と、上記光学位相差板の波長６５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （６５０）と波長５５０ｎｍの光に対する屈折率異方性Δｎ_Ｆ （５５０）の比であるΔｎ_Ｆ （６５０）／Δｎ_Ｆ （５５０）とが、
【０２３１】
【数１９】

【０２３２】
の関係を満たすように設定されていることを特徴としている。
【０２３３】
また、より好ましい構成としては、
【０２３４】
【数２０】

【０２３５】
の関係を満たすように設定されていることを特徴としている。
【０２３６】
これにより、本発明に係る第１、第２の液晶表示装置では、液晶表示素子の位相差変化を位相差板による補償機能のみの場合よりもさらに改善し、特に視角に依存した液晶画面の着色現象をより一層防止することができるので、このような位相差板と液晶表示素子とを含む液晶表示装置は、反転現象や反視角方向のコントラスト比の低下、着色現象を防止することができる。
【０２３７】
それゆえ、上記構成は、白黒表示におけるコントラスト比が観視者の視角方向によって影響されないため、液晶表示装置の表示画像の品質が格段に向上するという効果を奏する。
【０２３８】
また、上記した発明に係る各液晶表示装置においては、液晶層における液晶材料の、波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）が、０．０６０より大きく０．１２０より小さい範囲に設定されていることが好ましい。
【０２３９】
これにより、液晶表示素子に生じる視角に対応する位相差を解消することができるため、表示画面において、視角に依存して生じる着色現象はもちろんのこと、コントラスト変化、左右方向の反転現象等もさらに改善することができる。
【０２４０】
また、この場合、液晶層における液晶材料の、波長５５０ｎｍの光に対する屈折率異方性Δｎ（５５０）が、０．０７０以上０．０９５以下に範囲に設定されていることが好ましい。
【０２４１】
これにより、より一層、視角に依存して生じるコントラスト変化、左右方向の反転現象等を改善することができる。
【０２４２】
また、上記した本発明に係る各液晶表示装置においては、全ての位相差板において、屈折率楕円体の傾斜角が１５°から７５°の間に設定されていることが好ましい。
【０２４３】
このように、液晶表示装置に介在される全ての光学位相差板において、屈折率楕円体の傾斜角を１５°から７５°の間に設定することで、前述した本発明の備えた光学位相差板による位相差の補償機能を確実に得ることができ、視認性を確実に向上し得る。
【０２４４】
また、上記した本発明に係る各液晶表示装置においては、全ての光学位相差板において、主屈折率ｎ_ａ と主屈折率ｎ_ｂ との差と、光学位相差板の厚さｄとの積（ｎ_ａ −ｎ_ｂ ）×ｄが、８０ｎｍから２５０ｎｍの間に設定されていることが好ましい。
【０２４５】
このように、液晶表示装置に介在される全ての光学位相差板において、主屈折率ｎ_ａ と主屈折率ｎ_ｂ との差と、光学位相差板の厚さｄとの積（ｎ_ａ −ｎ_ｂ ）×ｄを、８０ｎｍから２５０ｎｍの間に設定することで、前述した本発明の備えた光学位相差板による位相差の補償機能を確実に得ることができ、視認性を確実に向上し得る。
【図面の簡単な説明】
【図１】本発明の実施の一形態に係る液晶表示装置の構成を分解して示す断面図である。
【図２】上記液晶表示装置における配向膜のラビング方向と正視角方向との関係を示す説明図である。
【図３】上記液晶表示装置の光学位相差板における主屈折率を示す斜視図である。
【図４】上記液晶表示装置における偏光板および光学位相差板の光学的な配置を液晶表示装置の各部を分解して示す斜視図である。
【図５】液晶分子の長軸と配向膜とがなす角であるプレティルト角を示す説明図である。
【図６】上記液晶表示装置の視角依存性を測定する測定系を示す斜視図である。
【図７】比較例１と該比較例１に対する比較例の液晶表示装置の透過率−液晶印加電圧特性を示すグラフである。
【図８】実施例１における液晶表示装置の透過率−液晶印加電圧特性を示すグラフである。
【図９】実施例１に対する比較例の液晶表示装置の透過率−液晶印加電圧特性を示すグラフである。
【図１０】上記液晶表示装置の液晶層に用いられる一液晶材料と一光学位相差板との波長に対するΔｎ（λ）／Δｎ（５５０）を示すグラフである。
【図１１】ＴＮ液晶表示素子における液晶分子のねじれ配向を示す模式図である。
【符号の説明】
１ 液晶表示素子
２・３ 光学位相差板
４・５ 偏光板（偏光子）
８ 液晶層
９・１２ ガラス基板（透光性基板）
１０・１３ 透明電極（透明電極層）
１１・１４ 配向膜[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which the viewing angle dependence of a display screen is improved by combining an optical retardation plate with a liquid crystal display element.
[0002]
[Prior art]
Liquid crystal display devices using nematic liquid crystal display elements have been widely used in numerical segment display devices such as watches and calculators, but recently, they have also been used in word processors, notebook personal computers, and in-vehicle liquid crystal televisions. Is being used.
[0003]
A liquid crystal display element generally has a light-transmitting substrate, on which electrode lines and the like are formed to turn on and off pixels. For example, in an active matrix type liquid crystal display device, active elements such as thin film transistors are formed on the substrate together with the above electrode lines as switching means for selectively driving a pixel electrode for applying a voltage to the liquid crystal. Further, in a liquid crystal display device that performs color display, a color filter layer of red, green, blue, or the like is provided on a substrate.
[0004]
As a liquid crystal display method used in the above-described liquid crystal display element, a different method is appropriately selected according to the twist angle of the liquid crystal. For example, an active drive type twisted nematic liquid crystal display method (hereinafter, referred to as a TN method) and a multiplex drive type super twisted nematic liquid crystal display method (hereinafter, referred to as an STN method) are well known.
[0005]
In the TN mode, display is performed by aligning nematic liquid crystal molecules in a twisted state by 90 ° and guiding light along the twisted direction. The STN system utilizes the fact that the transmittance near the threshold of the voltage applied to the liquid crystal changes sharply by expanding the twist angle of the nematic liquid crystal molecules to 90 ° or more.
[0006]
In the STN method, since the birefringence effect of liquid crystal is used, a specific color is given to the background of the display screen due to color interference. It is considered that the use of an optical compensator is effective in eliminating such inconvenience and performing monochrome display by the STN method. As a display method using an optical compensator, there are a double super twist nematic phase compensation method (hereinafter, referred to as a DSTN method) and a film type phase compensation method in which a film having optical anisotropy is arranged (hereinafter, a film addition type). System).
[0007]
The DSTN method uses a two-layer structure including a display liquid crystal cell and a liquid crystal cell which is twisted and aligned at a twist angle opposite to that of the display liquid crystal cell. The film addition type uses a structure in which a film having optical anisotropy is arranged. From the viewpoint of lightness and low cost, a film addition type system is considered to be effective. Since the black-and-white display characteristics have been improved by adopting such a phase compensation method, a color STN liquid crystal display device has been realized in which a color filter layer is provided on a STN display device to enable color display.
[0008]
On the other hand, the TN method is roughly classified into a normally black method and a normally white method. In the normally black mode, a pair of polarizing plates are disposed so that their polarization directions are parallel to each other, and black is displayed in a state where no on-voltage is applied to the liquid crystal layer (off state). In the normally white mode, a pair of polarizing plates are arranged so that their polarization directions are orthogonal to each other, and white is displayed in an off state. The normally white method is effective in terms of display contrast, color reproducibility, display angle dependency, and the like.
[0009]
By the way, in the TN liquid crystal display device described above, since the liquid crystal molecules have the refractive index anisotropy Δn and the liquid crystal molecules are inclined and oriented with respect to the upper and lower substrates, the viewing angle is low. There is a problem that the contrast of the displayed image changes depending on the viewing direction and the angle of the viewer, and the viewing angle dependency increases.
[0010]
FIG. 11 schematically shows a cross-sectional structure of the TN liquid crystal display element 31. This state shows a case where a voltage for displaying an intermediate color tone (hereinafter, referred to as an intermediate tone) is applied, and the liquid crystal molecules 32 are slightly rising. In the TN liquid crystal display element 31, the linearly polarized light 35 passing through the normal direction of the surface of the pair of substrates 33 and 34 and the linearly polarized light 36 and 37 passing with an inclination with respect to the normal direction are formed by liquid crystal molecules 32. The angles at which they intersect are different. Since the liquid crystal molecules 32 have a refractive index anisotropy Δn, normal light and extraordinary light are generated when the linearly polarized light 35, 36, 37 in each direction passes through the liquid crystal molecules 32. It is converted into elliptically polarized light, which is a source of viewing angle dependence.
[0011]
Further, inside the actual liquid crystal layer, the liquid crystal molecules 32 have different tilt angles between the vicinity of the intermediate portion between the substrate 33 and the substrate 34 and the vicinity of the substrate 33 or the substrate 34, and the liquid crystal molecules 32 The molecule 32 is twisted by 90 °.
[0012]
As described above, the linearly polarized lights 35, 36, and 37 passing through the liquid crystal layer receive various birefringence effects depending on their directions and angles, and exhibit complicated viewing angle dependence.
[0013]
As the above-described viewing angle dependency, specifically, a phenomenon in which a display image is colored at a certain angle or more when the viewing angle is inclined from the normal direction of the display screen to the normal viewing angle direction which is the downward direction of the display surface (hereinafter, referred to as A phenomenon called “coloring phenomenon”) or a phenomenon in which black and white are reversed (hereinafter, referred to as “reversal phenomenon”) occur. Also, when the viewing angle is inclined in the opposite viewing angle direction, which is the upper direction of the display screen, the contrast sharply decreases.
[0014]
Further, the above liquid crystal display device has a problem that the viewing angle becomes narrower as the display screen becomes larger. When a large liquid crystal display screen is viewed from the front direction at a short distance, colors displayed on the upper and lower parts of the display screen may be different due to the influence of viewing angle dependence. This is because the viewing angle of the entire display screen is increased, which is the same as viewing the display screen from an oblique direction.
[0015]
In order to improve such viewing angle dependency, it has been proposed to insert an optical retardation film (retardation film) as an optical element having optical anisotropy between the liquid crystal display element and one polarizing plate. (See, for example, JP-A-55-600 and JP-A-56-97318).
[0016]
This method uses an optical retardation plate in which light that has been converted from linearly polarized light to elliptically polarized light because it has passed through liquid crystal molecules having refractive index anisotropy is interposed on one or both sides of a liquid crystal layer having refractive index anisotropy. , The change in the phase difference between the normal light and the extraordinary light that occurs in the viewing angle is compensated, and the light is converted back into linearly polarized light, thereby improving the viewing angle dependency.
[0017]
As such an optical retardation plate, one in which one principal refractive index direction of an index ellipsoid is parallel to a normal direction of the surface of the optical retardation plate is described in, for example, JP-A-5-313159. ing. However, even if this optical retardation plate is used, there is a limit in improving the reversal phenomenon in the normal viewing direction.
[0018]
In order to eliminate the inversion phenomenon, for example, Japanese Patent Application Laid-Open No. S57-186735 discloses that each display pattern (pixel) is divided into a plurality of sections so that each section has independent viewing angle characteristics. A so-called pixel division method for controlling alignment is disclosed. According to this method, in each section, the liquid crystal molecules rise in directions different from each other, so that the viewing angle dependency can be eliminated. However, the problem that the contrast decreases when the viewing angle is tilted in the vertical direction is not solved.
[0019]
Japanese Patent Application Laid-Open Nos. 6-118406 and 6-194645 disclose a technique of combining an optical phase difference plate with the above-described pixel division method.
[0020]
In the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 6-118406, the contrast is improved by inserting an optically anisotropic film (optical retardation plate) between the liquid crystal panel and the polarizing plate. Have been. The compensating plate (optical retardation plate) disclosed in JP-A-6-194645 has almost no in-plane refractive index in a direction parallel to the compensating plate surface and a refractive index in a direction perpendicular to the compensating plate surface. Is set to be smaller than the in-plane refractive index, thereby having a negative refractive index. Therefore, when a voltage is applied, the positive refractive index generated in the liquid crystal display element can be compensated, and the viewing angle dependency can be reduced.
[0021]
However, even when this optical retardation plate is used for the pixel division method, it is difficult to uniformly generate a coloring phenomenon in an oblique direction of 45 ° when the viewing angle is inclined, and to uniformly suppress a decrease in contrast in the vertical direction.
[0022]
Therefore, one principal refractive index direction of the refractive index ellipsoid is parallel to the normal direction of the surface of the retardation plate, and the refractive index ellipsoid is generated depending on the viewing angle by using an unsloped optical retardation plate. There are limits to improving the contrast change, coloring phenomenon, and reversal phenomenon.
[0023]
Therefore, Japanese Patent Application Laid-Open No. 6-75116 discloses a method using an optical retardation plate in which the main refractive index direction of the refractive index ellipsoid is inclined with respect to the normal direction of the surface of the optical retardation plate. Proposed. In this method, the following two types of optical retardation plates are used.
[0024]
One is that, among the three main refractive indices of the refractive index ellipsoid, the direction of the minimum main refractive index is parallel to the surface, and one of the remaining two main refractive indices is the direction of the optical retardation plate. The surface is inclined at an angle of θ, and the other direction is also inclined at an angle of θ with respect to the normal direction of the optical retardation plate surface, and the value of θ is 20 ° ≦ θ ≦ 70 ° The optical retardation plate satisfies the following.
[0025]
The other is the three main refractive indices n of the index ellipsoid. _a , N _b , N _c Is n _a = N _c > N _b And the main refractive index n in the surface _a Or n _c The principal refractive index n parallel to the surface normal direction with the direction of _b And the main refractive index n in the surface _a Or n _c Is an optical retardation plate in which the refractive index ellipsoid is inclined clockwise or counterclockwise.
[0026]
Regarding the above two types of optical retardation plates, the former can be a uniaxial one and a biaxial one, respectively. In the latter case, not only one optical retardation plate is used, but also two optical retardation plates are combined and each main refractive index n _b Can be used such that the inclination directions of the are set to form an angle of 90 ° with each other.
[0027]
In a liquid crystal display device constituted by interposing at least one such optical retardation plate between a liquid crystal display element and a polarizing plate, a contrast change, a coloring phenomenon, and an inversion that occur depending on a viewing angle of a display image. The phenomenon can be improved to some extent.
[0028]
[Problems to be solved by the invention]
However, under the circumstances where today's liquid crystal display devices with a wider viewing angle and higher display quality are desired, further improvement in viewing angle dependency is required, and the optical position disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-75116 is disclosed. The use of a retardation plate is not always sufficient, and there is still room for improvement.
[0029]
The present invention has been made in view of the above-described problems, and an object of the present invention is to further improve viewing angle dependency in addition to the above-described compensation effect by the optical retardation plate, and particularly to effectively improve a coloring phenomenon. It is in.
[0030]
[Means for Solving the Problems]
In order to achieve the object of the present invention, each of the liquid crystal display devices according to the present invention has a liquid crystal display device in which a transparent electrode layer and an alignment film are formed on a pair of light-transmitting substrates, each of which has a twisted orientation of approximately 90 °. Liquid crystal display element in which the liquid crystal layer is sealed, a pair of polarizers disposed on both sides of the liquid crystal display element, and an optical phase difference interposed between the liquid crystal display element and the polarizer at least one sheet. Plate, the three principal refractive indices n of the index ellipsoid _a , N _b , N _c Is n _a = N _c > N _b And the main refractive index n in the surface _a Or n _c The principal refractive index n parallel to the surface normal direction with the direction of _b And the main refractive index n in the surface _c Or n _a Is tilted clockwise or counterclockwise to provide an optical retardation plate in which the refractive index ellipsoid is tilted, and is characterized by the following points.
[0031]
In the first liquid crystal display device, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn with respect to light having a wavelength of 450 nm. _L (450) and refractive index anisotropy Δn for light having a wavelength of 550 nm _L Δn which is the ratio of (550) _L (450) / Δn _L (550) and the refractive index anisotropy Δn of the optical retardation plate with respect to light having a wavelength of 450 nm. _F (450) and refractive index anisotropy Δn for light having a wavelength of 550 nm _F Δn which is the ratio of (550) _F (450) / Δn _F (550)
[0032]
(Equation 5)

[0033]
Is set to satisfy the relationship.
[0034]
In the second liquid crystal display device, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn with respect to light having a wavelength of 650 nm. _L (650) and refractive index anisotropy Δn for light having a wavelength of 550 nm _L Δn which is the ratio of (550) _L (650) / Δn _L (550) and the refractive index anisotropy Δn of the optical retardation plate for light having a wavelength of 650 nm. _F (650) and refractive index anisotropy Δn for light having a wavelength of 550 nm _F Δn which is the ratio of (550) _F (650) / Δn _F (550)
[0035]
(Equation 6)

[0036]
Is set to satisfy the relationship.
[0037]
According to the above configuration, the main refractive index n _a , N _b , N _c Is n _a = N _c > N _b And the main refractive index n _b Since the optical retardation plate in which the minor axis of the refractive index ellipsoid containing is tilted with respect to the normal direction of the surface of the optical retardation plate is interposed between the liquid crystal layer and the polarizer, linearly polarized light is birefringent. When normal light and extraordinary light are generated by passing through a liquid crystal layer having properties and are converted into elliptically polarized light due to the phase difference, the phase difference between the normal light and the extraordinary light occurs according to the viewing angle. Is compensated by this optical retardation plate.
[0038]
However, even if such a compensation function requires further improvement of the viewing angle dependency, it cannot be said that it is necessarily sufficient. Of the refractive index anisotropy Δn of the optical retardation plate with respect to the wavelength of light and the change of the refractive index anisotropy Δn of the optical retardation plate with respect to the wavelength of the light affect the coloring of the liquid crystal screen depending on the viewing angle. This led to the completion of the present invention.
[0039]
By setting the change of the refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer with respect to the wavelength of light in any one of the ranges described in the first and second liquid crystal display devices, it is possible to satisfy the demand in a normal liquid crystal display device. At a viewing angle of 50 °, although there is some coloring, it was possible to sufficiently withstand use from any direction, and it was possible to further prevent the coloring of the screen. It should be noted that the contrast change and the inversion phenomenon can be improved as compared with the case where only the compensation function of the retardation plate is used.
[0040]
In a liquid crystal display device having a wider viewing angle such as a viewing angle of 70 °, the range of change in the refractive index anisotropy Δn of the liquid crystal material with respect to the wavelength of light is preferably set to the following range.
[0041]
That is,
[0042]
(Equation 7)

[0043]
Is set so as to satisfy the relationship.
[0044]
Or
[0045]
(Equation 8)

[0046]
Is set so as to satisfy the relationship.
[0047]
By setting any of these ranges, no coloring phenomenon can be obtained even when viewed from all directions at a viewing angle of 70 ° required for a liquid crystal display device having a wide viewing angle.
[0048]
In each of the above-described liquid crystal display devices of the present invention, the refractive index anisotropy Δn (550) of the liquid crystal material in the liquid crystal layer with respect to light having a wavelength of 550 nm is set to a range larger than 0.060 and smaller than 0.120. Is preferred.
[0049]
This is because when the refractive index anisotropy Δn (550) of the liquid crystal material is 0.060 or less or 0.120 or more with respect to light having a wavelength of 550 nm, which is the central region of the visible light region, the inversion phenomenon and the contrast ratio depend on the viewing angle direction. This is because it has been confirmed that a decrease in the density occurs. Therefore, by setting the refractive index anisotropy Δn (550) of the liquid crystal material to light having a wavelength of 550 nm in a range larger than 0.060 and smaller than 0.120, the phase difference corresponding to the viewing angle generated in the liquid crystal display element can be reduced. Therefore, not only a coloring phenomenon depending on a viewing angle but also a contrast change, a left-right inversion phenomenon, and the like can be further improved on the liquid crystal screen.
[0050]
In this case, by further setting the refractive index anisotropy Δn (550) of the liquid crystal material in the liquid crystal layer with respect to light having a wavelength of 550 nm in a range of 0.070 or more and 0.095 or less, a viewing angle generated in the liquid crystal display element is obtained. Since the phase difference corresponding to the above can be more effectively eliminated, it is possible to reliably improve the contrast change and the left-right inversion phenomenon in the liquid crystal display image.
[0051]
In each of the liquid crystal display devices of the present invention described above, it is preferable that the inclination angle of the refractive index ellipsoid is set between 15 ° and 75 ° in all the optical retardation plates.
[0052]
As described above, in all the optical retardation plates interposed in the liquid crystal display device, by setting the inclination angle of the refractive index ellipsoid between 15 ° and 75 °, the optical retardation provided by the present invention described above is provided. The function of compensating for the phase difference by the plate can be reliably obtained.
[0053]
In each of the liquid crystal display devices of the present invention described above, the main refractive index n _a And the main refractive index n _b (N) and the thickness d of the optical retardation plate (n _a -N _b ) × d is preferably set between 80 nm and 250 nm.
[0054]
Thus, in all the optical retardation plates interposed in the liquid crystal display device, the main refractive index n _a And the main refractive index n _b (N) and the thickness d of the optical retardation plate (n _a -N _b By setting (x) between 80 nm and 250 nm, it is possible to reliably obtain the phase difference compensation function of the optical phase difference plate according to the present invention described above.
[0055]
BEST MODE FOR CARRYING OUT THE INVENTION
One embodiment of the present invention will be described below with reference to FIGS.
[0056]
First, before describing an embodiment of the present invention, a liquid crystal display device of a reference example will be described. As shown in FIG. 1, the liquid crystal display device includes a liquid crystal display element 1, a pair of optical retardation plates 2 and 3, and a pair of polarizing plates (polarizers) 4.5.
[0057]
The liquid crystal display element 1 has a structure in which a liquid crystal layer 8 is interposed between electrode substrates 6 and 7 arranged opposite to each other. In the electrode substrate 6, a transparent electrode 10 made of ITO (indium tin oxide) is formed on a surface of a glass substrate (translucent substrate) 9 serving as a base on the liquid crystal layer 8 side, and an alignment film 11 is formed thereon. ing. In the electrode substrate 7, a transparent electrode 13 made of ITO is formed on a surface of a glass substrate (translucent substrate) 12 serving as a base on a liquid crystal layer 8 side, and an alignment film 14 is formed thereon.
[0058]
For the sake of simplicity, FIG. 1 shows a configuration for two pixels, but in the entire liquid crystal display element 1, strip-shaped transparent electrodes 10 and 13 having a predetermined width are provided at predetermined intervals on the glass substrates 9 and 12, respectively. The glass substrates 9 and 12 are formed so as to be orthogonal to each other when viewed from a direction perpendicular to the substrate surface. A portion where the transparent electrodes 10 and 13 intersect corresponds to a pixel for displaying, and these pixels are arranged in a matrix in the entire liquid crystal display device.
[0059]
The electrode substrates 6 and 7 are bonded together with a sealing resin 15, and a liquid crystal layer 8 is sealed in a space formed by the electrode substrates 6 and 7 and the sealing resin 15. A voltage based on display data is applied to the liquid crystal layer 8 from the driving circuit (voltage applying means) 17 via the transparent electrodes 10 and 13.
[0060]
Although the details will be described later, in the present liquid crystal display device, the pretilt angle of the liquid crystal layer 8 is set so as to provide a combination having a function of compensating a phase difference by the optical phase difference plates 2 and 3 and the best characteristic. Have been.
[0061]
In the liquid crystal display device, a liquid crystal cell 16 is a unit formed by forming the optical retardation plates 2 and 3 and the polarizing plates 4 and 5 on the liquid crystal display element 1.
[0062]
The alignment films 11 and 14 are rubbed in advance so that the intervening liquid crystal molecules are twisted at about 90 °. As shown in FIG. 2, the rubbing direction R1 of the alignment film 11 and the rubbing direction R2 of the alignment film 14 are set to directions orthogonal to each other.
[0063]
The optical retardation plates 2 and 3 are interposed between the liquid crystal display element 1 and the polarizing plates 4 and 5 disposed on both sides of the liquid crystal display element 1. The optical retardation plates 2 and 3 are formed by cross-linking a discotic liquid crystal in a tilted or hybrid orientation on a support made of a transparent organic polymer and cross-linking. As a result, a later-described refractive index ellipsoid in the optical retardation plates 2 and 3 is formed so as to be inclined with respect to the optical retardation plates 2 and 3.
[0064]
As a support for the optical retardation plates 2 and 3, triacetyl cellulose (TAC), which is generally often used for a polarizing plate, is highly reliable and suitable. In addition, a colorless and transparent organic polymer film having excellent environmental resistance and chemical resistance such as polycarbonate (PC) and polyethylene terephthalate (PET) is suitable.
[0065]
As shown in FIG. 3, the optical retardation plates 2 and 3 have main refractive indices n in three different directions. _a ・ N _b ・ N _c have. Main refractive index n _a Is the same as the y coordinate axis among the coordinate axes at the orthogonal coordinates xyz. Main refractive index n _b Is inclined by θ in the direction of arrow A with respect to the z-coordinate axis (normal direction of the surface) perpendicular to the surface corresponding to the screen in the optical retardation plates 2 and 3.
[0066]
Each of the optical retardation plates 2 and 3 has a main refractive index of n _a = N _c > N _b Satisfies the relationship. Thus, since there is only one optical axis, the optical retardation plates 2 and 3 have uniaxiality and the refractive index anisotropy becomes negative. The first retardation value of the optical retardation plates 2 and 3 (n _c -N _a ) × d is n _a = N _c Therefore, it is almost 0 nm. The second retardation value (n _c -N _b ) × d is set to an arbitrary value within the range of 80 nm to 250 nm. The second retardation value (n _c -N _b By setting x) in such a range, the phase difference compensation function of the optical phase difference plates 2 and 3 can be reliably obtained. Note that the above n _c -N _a And n _c -N _b Represents the refractive index anisotropy Δn, and d represents the thickness of the optical retardation plates 2 and 3.
[0067]
The main refractive index n of the optical retardation plates 2 and 3 _b Is inclined, that is, the inclination angle θ of the refractive index ellipsoid is set to an arbitrary value within a range of 15 ° ≦ θ ≦ 75 °. By setting the inclination angle θ in such a range, the phase difference compensating function of the optical retardation plates 2 and 3 can be reliably obtained regardless of whether the inclination direction of the index ellipsoid is clockwise or counterclockwise. be able to.
[0068]
The arrangement of the optical retardation plates 2 and 3 may be such that only one of the optical retardation plates 2 and 3 is arranged on one side, or the optical retardation plates 2 and 3 may be overlapped on one side. It can also be placed. Further, three or more optical retardation plates can be used.
[0069]
Then, as shown in FIG. 4, in the liquid crystal display device of the reference example, the polarizing plates 4 and 5 of the liquid crystal display element 1 have their absorption axes AX. ₁ ・ AX ₂ Is the rubbing direction R of the alignment films 11 and 14 (see FIG. 1). ₁ ・ R ₂ Are arranged in parallel with each other. In the present liquid crystal display device, the rubbing direction R ₁ ・ R ₂ Are orthogonal to each other, the absorption axis AX ₁ ・ AX ₂ Are also orthogonal to each other.
[0070]
Here, as shown in FIG. 3, the main refractive index n inclined in a direction for giving anisotropy to the optical retardation plates 2 and 3 _b Is defined as the direction projected on the surfaces of the optical retardation plates 2 and 3. As shown in FIG. 4, the optical retardation plate 2 is moved in a direction D (direction D). ₁ ) Is the rubbing direction R ₁ And the optical phase difference plate 3 is oriented in the direction D (direction D). ₂ ) Is the rubbing direction R ₂ It is arranged so that it may become parallel.
[0071]
By the arrangement of the optical retardation plates 2 and 3 and the polarizing plates 4 and 5 as described above, the present liquid crystal display device performs so-called normally white display in which light is transmitted and white display is performed when the liquid crystal display is off.
[0072]
Generally, in an optically anisotropic body such as a liquid crystal or an optical retardation film (retardation film), the main refractive index n in the three-dimensional direction as described above. _a ・ N _c ・ N _b Is represented by a refractive index ellipsoid. The refractive index anisotropy Δn varies depending on the direction in which the refractive index ellipsoid is observed.
[0073]
Next, the setting of the pretilt angle in the liquid crystal layer 8 will be described in detail.
[0074]
As shown in FIG. 5, the pretilt angle is an angle ψ between the long axis of the liquid crystal molecules 20 and the alignment film 14 (11), and depends on the combination of the rubbing with the alignment films 11 and 14 and the liquid crystal material. Is to be determined.
[0075]
As described above, in the liquid crystal display device of the reference example, the pretilt angle of the liquid crystal layer 8 is set so as to provide a combination having a function of compensating the phase difference by the optical retardation plates 2 and 3 and the best characteristic. More specifically, the pretilt angle is a halftone display state in which a voltage close to the threshold voltage of the liquid crystal is applied to the liquid crystal. The range is set so that tone inversion does not occur. Hereinafter, a halftone close to white is referred to as a white gradation.
[0076]
On the other hand, it has been experimentally confirmed that as the pretilt angle increases, the grayscale inversion in the anti-viewing angle direction at the time of white gradation does not occur. It was also confirmed that a sharp decrease in luminance at the time of white gradation occurred. That is, in setting the pretilt angle, it is necessary to set the pretilt angle within a range in which a sharp decrease in luminance in the normal viewing angle direction does not occur during white gradation.
[0077]
Specifically, as the alignment films 11 and 14 and the liquid crystal material, a combination of an alignment film and a liquid crystal material having a pretilt angle of more than 2 ° and less than 12 ° is used. In this case, it is more preferable to use a combination of an alignment film and a liquid crystal material such that the pretilt angle is in the range of 4 ° to 10 °.
[0078]
By setting the pretilt angle within the range of more than 2 ° and less than 12 ° in this manner, the problem arises at the viewing angle of 50 ° required for a normal liquid crystal display device, which is a problem in the anti-viewing angle direction at the time of white gradation, which becomes a problem. , Which can sufficiently withstand use from any direction.
[0079]
In particular, by setting the pretilt angle within the range of 4 ° or more and 10 ° or less, there can be no grayscale inversion in the anti-viewing angle direction at the time of white grayscale at 70 °.
[0080]
Further, in the liquid crystal display device of the reference example, the liquid crystal material in the liquid crystal layer 8 is designed such that the refractive index anisotropy Δn (550) for light having a wavelength of 550 nm is in a range larger than 0.060 and smaller than 0.120. Is selected. In this case, it is more preferable to use a liquid crystal material whose Δn (550) is designed to be in a range of 0.070 or more and 0.095 or less.
[0081]
Accordingly, in addition to the compensation function of the phase difference by the optical retardation plates 2 and 3 and the compensation function by setting the pretilt angle in the above range, the contrast ratio in the anti-viewing angle direction is reduced, and the phenomenon of reversal in the horizontal direction is prevented. It is possible to further improve.
[0082]
As described above, in the liquid crystal display device of the reference example, the three main refractive indices n of the refractive index ellipsoid are provided between the liquid crystal display element 1 and the polarizing plates 4 and 5. _a , N _b , N _c Is n _a = N _c > N _b And the main refractive index n in the surface _a Or n _c The principal refractive index n parallel to the surface normal direction with the direction of _b And the main refractive index n in the surface _c Or n _a Is tilted clockwise or counterclockwise to provide a liquid crystal display device having the optical retardation plates 2 and 3 in which the refractive index ellipsoid is inclined. Is set in a range in which gradation inversion in the anti-viewing angle direction does not occur in a halftone display state in which a voltage close to the threshold voltage of the liquid crystal is applied to the liquid crystal.
[0083]
Accordingly, in addition to the function of compensating the phase difference corresponding to the viewing angle generated in the liquid crystal display element 1 by the above-mentioned optical retardation plates 2 and 3, the compensation function by setting the pretilt angle in the above-mentioned range allows the viewing angle-dependent countermeasure. It is possible to particularly effectively improve the reversal phenomenon that occurs at the time of white gradation in the viewing angle direction (because of normally white display), and at the same time, to improve the contrast change and display a high-quality image. .
[0084]
In addition, in this liquid crystal display device, a liquid crystal material used in the liquid crystal layer 8 is designed so that the refractive index anisotropy Δn (550) for light having a wavelength of 550 nm is larger than 0.060 and smaller than 0.120. Therefore, in addition to the compensation function of the phase difference by the optical retardation plates 2 and 3 and the compensation function by setting the pretilt angle in the above range, the contrast ratio in the anti-viewing angle direction decreases, and the reversal phenomenon in the horizontal direction. Can be further improved.
[0085]
Here, the liquid crystal display device of normally white display has been described as an example. However, in the liquid crystal display device of normally black display as well, the pretilt angle of the liquid crystal display device is adjusted in accordance with the compensation effect of the optical retardation plates 2 and 3. In the halftone display (black gradation) in which a voltage close to the threshold voltage is applied to the liquid crystal, a range in which gradation inversion in the anti-viewing angle direction does not occur is obtained, and the same effect as described above can be obtained by obtaining a compensation effect. Obtainable.
[0086]
Although the simple matrix type liquid crystal display device is described here, the present invention is also applicable to an active matrix type liquid crystal display device using active switching elements such as TFTs.
[0087]
Next, a liquid crystal display device of another reference example will be described with reference to FIG. For convenience of explanation, members having the same functions as those shown in the liquid crystal display device of the above-described reference example (hereinafter referred to as a first reference example) are denoted by the same reference numerals, and description thereof is omitted. .
[0088]
The liquid crystal display device of the second embodiment described here has substantially the same configuration as the liquid crystal display device of FIG. 1 which is the first embodiment described above. The difference is that, in the liquid crystal display device of the first reference example, the pretilt angle of the liquid crystal layer 8 is set so as to provide a combination having a function of compensating for a phase difference by the optical retardation plates 2 and 3 and the best characteristic. In the halftone display state in which a voltage close to the threshold voltage of the liquid crystal is applied to the layer 8, the range is set to a range in which gradation inversion in the anti-viewing angle direction does not occur. In the liquid crystal display device of the second reference example, An application for displaying a halftone obtained by applying a voltage close to the threshold voltage of the liquid crystal to the liquid crystal layer 8 so that the combination having the phase difference compensating function of the phase difference plates 2 and 3 and the best characteristic can be obtained. The point is that the voltage value is set in a range in which gradation inversion in the anti-viewing angle direction does not occur in the halftone display state.
[0089]
Hereinafter, this point will be described in detail. Since the liquid crystal display device of the second reference example is a normally white display, a halftone display state in which a voltage close to the threshold voltage of the liquid crystal is applied to the liquid crystal, that is, an applied voltage value for performing white gradation, It is set in a range in which gradation inversion in the anti-viewing angle direction does not occur when the voltage is applied.
[0090]
On the other hand, it was experimentally confirmed that the lower the transmittance at the time of white gradation, the more the grayscale inversion in the opposite viewing angle direction at the time of white gradation does not occur. However, if the transmittance is set too low, Brightness sharply decreases in the normal viewing angle direction and the left and right direction. That is, in setting the liquid crystal applied voltage that determines the transmittance at the time of white gradation, it is necessary to set the voltage in a range in which a sharp decrease in luminance in the normal viewing direction and the left and right directions does not occur at the time of white gradation.
[0091]
Specifically, the liquid crystal application voltage at the time of white gradation is set so as to obtain a transmittance greater than 85% with respect to the transmittance 100% in the off state where the liquid crystal application voltage is zero. In this case, more preferably, the liquid crystal application voltage at the time of white gradation is set so as to obtain a transmittance in a range of 90% or more and 97% or less with respect to a transmittance of 100% in an off state.
[0092]
By setting the liquid crystal application voltage at the time of white gradation so as to obtain a transmissivity greater than 85% with respect to a transmissivity of 100% in the off state, the viewing angle 50 ° required for a normal liquid crystal display device is obtained. In this case, there is no grayscale inversion in the anti-viewing angle direction at the time of white grayscale that causes a problem, and it is possible to sufficiently endure use in any direction.
[0093]
In particular, by setting the liquid crystal applied voltage at the time of white gradation to be in a range of 90% or more and 97% or less with respect to the transmittance of 100% in the off state, at a viewing angle of 70 °, the opposite viewing angle direction at the time of white gradation is obtained. There can be no gradation inversion at all.
[0094]
That is, the liquid crystal display device of the second reference example has three main refractive indices n of the refractive index ellipsoid between the liquid crystal display element 1 and the polarizing plates 4 and 5. _a , N _b , N _c Is n _a = N _c > N _b And the main refractive index n in the surface _a Or n _c The principal refractive index n parallel to the surface normal direction with the direction of _b And the main refractive index n in the surface _c Or n _a Is tilted clockwise or counterclockwise, so that in the liquid crystal display device having the optical retardation plates 2 and 3 in which the refractive index ellipsoid is tilted, the liquid crystal display device is close to the threshold voltage of the liquid crystal. In this configuration, an applied voltage value for performing a halftone display state in which a voltage is applied to the liquid crystal is set in a range in which gradation inversion in the anti-viewing angle direction does not occur when the voltage is applied.
[0095]
Thus, the phase difference corresponding to the viewing angle generated in the liquid crystal display element 1 is compensated by the optical retardation plates 2 and 3 and the compensation function by setting the liquid crystal application voltage at the time of white gradation in the above range is achieved. It is possible to particularly effectively improve the reversal phenomenon that occurs at the time of white gradation in the anti-viewing angle direction depending on the viewing angle (because it is a normally white display), and at the same time, to improve the contrast change, Display quality images.
[0096]
Further, also in the liquid crystal display device of the second reference example, the liquid crystal material in the liquid crystal layer 8 is designed so that the refractive index anisotropy Δn (550) with respect to light having a wavelength of 550 nm is larger than 0.060 and smaller than 0.120. More preferably, by using a liquid crystal material designed so that Δn (550) is in the range of 0.070 or more and 0.095 or less, the phase difference compensation function of the optical phase difference plates 2 and 3 is achieved. In addition to the compensation function by setting the liquid crystal application voltage at the time of white gradation in the above range, it is possible to further reduce the contrast ratio in the anti-viewing angle direction and the left-right inversion phenomenon.
[0097]
Although the liquid crystal display device of normally white display has been described as an example here, the liquid crystal display device of normally black display can also adjust the threshold voltage of the liquid crystal in accordance with the compensation effect of the optical retardation plates 2 and 3. The liquid crystal applied voltage for displaying a halftone (black gradation) obtained by applying a voltage close to the liquid crystal to the liquid crystal is set in a range in which the grayscale inversion in the anti-viewing angle direction does not occur in the halftone. By obtaining the effect, the same effect as described above can be obtained.
[0098]
Further, similarly to the liquid crystal display device of the first reference example described above, in addition to the simple matrix type liquid crystal display device, an active matrix type liquid crystal display device using an active switching element such as a TFT can be applied. .
[0099]
Hereinafter, a liquid crystal display device according to an embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those shown in the first and second reference examples are denoted by the same reference numerals, and description thereof is omitted.
[0100]
The liquid crystal display device according to the present embodiment (hereinafter, this liquid crystal display device) has substantially the same configuration as the liquid crystal display device of the first reference example shown in FIG. The difference is that, in the liquid crystal display device of the first reference example, the pretilt angle of the liquid crystal layer 8 is set so as to provide a combination having a function of compensating for a phase difference by the optical retardation plates 2 and 3 and the best characteristic. In the halftone display state in which a voltage close to the threshold voltage of the liquid crystal is applied to the layer 8, the range is set so that gradation inversion in the anti-viewing angle direction does not occur. The change in the refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer 8 with respect to the wavelength of light and the optical retardation of the optical retardation plate so as to provide a combination having the best characteristic and the compensation function of the phase difference by the retardation plates 2 and 3. The point is that the degree of change of the refractive index anisotropy Δn with respect to the wavelength of light is set in a range in which coloring of the liquid crystal screen depending on the viewing angle does not occur.
[0101]
Hereinafter, this point will be described in detail. The degree of change between the change in the refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer 8 with respect to the wavelength of light and the change in the refractive index anisotropy Δn of the optical retardation plate with respect to the light wavelength is determined by the viewing angle-dependent liquid crystal. Setting the screen to a range in which coloring does not occur specifically means that the optical retardation plates 2 and 3 are combined in such a manner as to satisfy at least one of the following setting conditions of (1) and (2). And a liquid crystal material may be used.
[0102]
{Circle around (1)} The refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer 8 with respect to light having a wavelength of 450 nm. _L (450) and refractive index anisotropy Δn for light having a wavelength of 550 nm _L Δn which is the ratio of (550) _L (450) / Δn _L (550) and the refractive index anisotropy Δn of the optical retardation plates 2 and 3 with respect to light having a wavelength of 450 nm. _F (450) and refractive index anisotropy Δn for light having a wavelength of 550 nm _F Δn which is the ratio of (550) _F (450) / Δn _F (550) and
[0103]
(Equation 9)

[0104]
May be set so as to satisfy the relationship. And, more preferably,
[0105]
(Equation 10)

[0106]
More preferably,
[0107]
(Equation 11)

[0108]
Is set so as to satisfy the relationship.
[0109]
{Circle around (2)} Refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer 8 with respect to light having a wavelength of 650 nm. _L (650) and refractive index anisotropy Δn for light having a wavelength of 550 nm _L Δn which is the ratio of (550) _L (650) / Δn _L (550) and the refractive index anisotropy Δn of the optical retardation plates 2 and 3 with respect to light having a wavelength of 650 nm. _F (650) and refractive index anisotropy Δn for light having a wavelength of 550 nm _F Δn which is the ratio of (550) _F (650) / Δn _F (550) and
[0110]
(Equation 12)

[0111]
May be set so as to satisfy the relationship. And, more preferably,
[0112]
(Equation 13)

[0113]
More preferably,
[0114]
[Equation 14]

[0115]
Is set so as to satisfy the relationship.
[0116]
By using a liquid crystal material and an optical retardation plate designed to satisfy at least one of the above (1) and (2), display by the phase difference compensation function by the optical retardation plates 2 and 3 is performed. Not only the contrast change, reversal phenomenon, and coloring phenomenon that occur depending on the viewing angle of the screen can be improved, but also the coloring phenomenon of the display screen can be particularly effectively improved.
[0117]
More specifically, by satisfying at least one of the wider ranges of (1) and (2), the color is slightly colored at a viewing angle of 50 ° required in a normal liquid crystal display device, but from any direction. Can be sufficiently used. Further, by satisfying at least one of the more preferable ranges in the above (1) and (2), although there is some coloring at a viewing angle of 60 °, it is possible to sufficiently endure use in any direction. In particular, by satisfying at least one of the more preferable ranges in the above (1) and (2), no coloring can be obtained from any direction.
[0118]
Further, by satisfying at least one of (1) and (2), the contrast change and the inversion phenomenon can be improved as compared with the case where only the compensation function of the optical retardation plates 2 and 3 is used.
[0119]
FIG. 10 shows Δn for each wavelength (λ) in a combination of a liquid crystal material that can be used for the liquid crystal layer 8 and an optical retardation plate that can be used for the optical retardation plates 2 and 3 in the present liquid crystal display device. (Λ) / Δn (550). A curve a indicated by a solid line is Δn (λ) / Δn (550) with respect to the wavelength (λ) of one liquid crystal material, and a curve b indicated by a chain line is Δn with respect to the wavelength (λ) of one optical retardation plate. (Λ) / Δn (550).
[0120]
As described above, in the liquid crystal display device of the present embodiment, the three main refractive indexes n of the refractive index ellipsoid are provided between the liquid crystal display element 1 and the polarizing plates 4 and 5. _a , N _b , N _c Is n _a = N _c > N _b And the main refractive index n in the surface _a Or n _c The principal refractive index n parallel to the surface normal direction with the direction of _b And the main refractive index n in the surface _c Or n _a Is tilted clockwise or counterclockwise to provide the liquid crystal material in the liquid crystal layer 8 in the liquid crystal display device having the optical retardation plates 2 and 3 in which the refractive index ellipsoid is inclined. The degree of change between the change in the refractive index anisotropy Δn of the optical retardation plate with respect to the wavelength of the light and the change in the refractive index anisotropy Δn of the optical retardation plate with respect to the wavelength of the light does not cause coloring of the liquid crystal screen depending on the viewing angle. The configuration is set to a range.
[0121]
Thereby, the phase difference corresponding to the viewing angle generated in the liquid crystal display element 1 is compensated by the optical retardation plates 2 and 3, and the change in the refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer 8 with respect to the wavelength of light. The compensation function by setting the degree of change of the refractive index anisotropy Δn of the optical retardation plate with respect to the wavelength of light within the above-described range makes it possible to particularly effectively improve the coloring of the display screen depending on the viewing angle. At the same time, the contrast change and the gradation inversion can be improved, and a high-quality image can be displayed.
[0122]
Further, also in the liquid crystal display device of the present embodiment, as the liquid crystal material in the liquid crystal layer 8, the refractive index anisotropy Δn (550) for light having a wavelength of 550 nm is designed to be in a range larger than 0.060 and smaller than 0.120. More preferably, by using a liquid crystal material designed such that Δn (550) is in the range of 0.070 or more and 0.095 or less, the function of compensating for the phase difference by the optical retardation plates 2 and 3 is achieved. In addition to the compensation function by setting the degree of change in the above range, it is possible to further reduce the contrast ratio in the anti-viewing angle direction and the left-right inversion phenomenon.
[0123]
Although the liquid crystal display device of normally white display has been described as an example here, the same effect as described above can be obtained in a liquid crystal display device of normally black display.
[0124]
Further, similarly to the liquid crystal display device of the first embodiment, an active matrix type liquid crystal display device using an active switching element such as a TFT can be applied in addition to the simple matrix type liquid crystal display device.
[0125]
【Example】
Next, an example supporting the effect of the liquid crystal display device according to the embodiment of the present invention will be described.
[0126]
(Reference Example 1)
This embodiment is for supporting the effects of the liquid crystal display devices according to the first and second embodiments, and here, the alignment film 11 of the liquid crystal cell 16 in the liquid crystal display device of FIG. In step 14, an Optmer AL (trade name) manufactured by Nippon Synthetic Rubber Co., Ltd. was used. Five sample cells # 1 to # 7 were prepared by using a liquid crystal material of °, 10.0 °, 11.0 °, and 12.0 ° and having a cell thickness (thickness of the liquid crystal layer 8) of 5 μm.
[0127]
The pretilt angles of these sample cells # 1 to # 7 were measured by preparing a homogeneous cell into which the materials of sample cells # 1 to # 7 were injected, and using a pretilt angle measuring device NSMAP-3000LCD (manufactured by Sigma Koki Co., Ltd.). .
[0128]
Further, as the optical retardation plates 2 and 3 in the sample cells # 1 to # 7, a discotic liquid crystal is applied to a transparent support (for example, triacetyl cellulose (TAC) or the like), and the discotic liquid crystal is tilt-aligned. The first retardation value is 0 nm, the second retardation value is 100 nm, and the main refractive index n _b Is inclined so as to be about 20 ° in the direction indicated by arrow A with respect to the z-axis direction in the xyz-axis coordinates, and similarly, the main refractive index n _c Has an angle of about 20 ° with respect to the x-axis in the direction shown by the arrow B (that is, the index ellipsoid has an inclination angle θ = 20 °).
[0129]
Tables 1 to 7 show the results of a visual test performed on these sample cells # 1 to # 7 under white light with variously applied voltages during white gradation.
[0130]
[Table 1]

[0131]
Table 1 shows that as a liquid crystal applied voltage for obtaining a white gradation, the transmittance in the normal direction of the surface of the liquid crystal cell 16 in the off state where the applied voltage to the liquid crystal is zero is 100%, and the transmittance is 100%. Is a result obtained by setting a value obtained in the normal direction for each sample cell and examining a display state at the time of white gradation.
[0132]
From Table 1, when the voltage at the time of white gradation is set with the transmittance set to 100%, in the sample cells # 4 and # 5 where the pretilt angles are 5.0 ° and 10.0 °, the viewing angle is set to 70 ° and Even when viewed from the viewing angle direction, no gradation inversion was confirmed, and the image quality was good.
[0133]
In sample cell # 2 with a pretilt angle of 3.0 ° and sample cell # 3 with a pretilt angle of 4.0 °, tone reversal was confirmed up to a viewing angle of 60 ° even when viewed from the opposite viewing angle direction. However, when the viewing angle was 70 °, the sample cell # 2 was confirmed to have a tone reversal that could withstand use. In the sample cell # 3, there was no tone reversal. Crushed. However, in each case, the viewing angle was 70 ° and it was sufficiently usable.
[0134]
In sample cell # 6 with a pretilt angle of 11.0 °, good image quality was obtained up to a viewing angle of 60 °, but when viewed from a normal viewing angle direction at a viewing angle of 70 °, the luminance was so low that it could not withstand use. Was confirmed.
[0135]
On the other hand, in the sample cell # 1 in which the pretilt angle was 2.0 °, gradation inversion was confirmed when viewed from the anti-viewing angle direction even at a viewing angle of 50 °, and the pretilt angle was set to 12.0 °. In sample cell # 7, it was confirmed that even at a viewing angle of 50 °, the brightness decreased so as to be unusable when viewed from the normal viewing angle direction.
[0136]
[Table 2]

[0137]
Table 2 shows the results obtained by setting the voltage during white gradation for each sample cell assuming that the transmittance with respect to the transmittance in the off state is 97%.
[0138]
From Table 2, when the voltage at the time of white gradation is set with the transmittance being 97%, the sample cells # 3, # 4, # 5 with the pretilt angles of 4.0 °, 5.0 °, 10.0 ° are set. As a result, even when the viewing angle was set to 70 ° and viewed from the anti-viewing angle direction, no gradation inversion was confirmed, and the image quality was excellent.
[0139]
In sample cell # 2 in which the pretilt angle was 3.0 °, tone reversal was not confirmed even when viewed from the anti-viewing angle direction up to a viewing angle of 50 °, and good image quality was obtained. Was. However, since no grayscale inversion was confirmed, it could be used even at a viewing angle of 60 °. In sample cell # 6 with a pretilt angle of 11.0 °, good image quality was obtained up to a viewing angle of 50 °, but when viewed from a normal viewing angle direction at a viewing angle of 60 °, the brightness was so low that it could not withstand use. It was confirmed that.
[0140]
On the other hand, in the sample cell # 1 in which the pretilt angle was 2.0 °, gradation inversion was confirmed even when the viewing angle was 50 ° when viewed from the opposite viewing angle direction. Further, in the sample cell # 7 in which the pretilt angle was 12.0 °, even at a viewing angle of 50 °, a decrease in luminance that would not withstand use was confirmed when viewed from the normal viewing angle direction.
[0141]
[Table 3]

[0142]
Table 3 shows the results obtained by setting the voltage at the time of white gradation for each sample cell assuming that the transmittance with respect to the transmittance in the off state is 95%. This was the same result as in Table 2 in which the voltage was set at a transmittance of 95%.
[0143]
[Table 4]

[0144]
Table 4 shows the results obtained by setting the voltage at the time of white gradation for each sample cell assuming that the transmittance with respect to the transmittance in the off state is 92%.
[0145]
From Table 4, when the voltage at the time of white gradation is set with the transmittance being 92%, the sample cells # 3, # 4, # 5 with the pretilt angles of 4.0 °, 5.0 °, 10.0 ° are set. As a result, even when the viewing angle was set to 70 ° and viewed from the anti-viewing angle direction, no gradation inversion was confirmed, and the image quality was excellent.
[0146]
In sample cell # 2 in which the pretilt angle was 3.0 °, tone reversal was not confirmed when viewed from the anti-viewing angle direction up to a viewing angle of 60 °, but the image quality was good, but the tone was reversed at a viewing angle of 70 °. did. However, it was of such a degree that it could be used. In sample cell # 6 with a pretilt angle of 11.0 °, good image quality was obtained up to a viewing angle of 50 °, but when viewed from a normal viewing angle direction at a viewing angle of 60 °, the brightness was so low that it could not withstand use. Was confirmed. In sample cell # 1 in which the pretilt angle was 2.0 °, the gradation was inverted at a viewing angle of 50 °, but it was of a degree that could be used.
[0147]
On the other hand, in sample cell # 7 in which the pretilt angle was 12.0 °, even at a viewing angle of 50 °, a decrease in luminance was found that was unusable when viewed from the normal viewing angle direction.
[0148]
[Table 5]

[0149]
Table 5 shows the results obtained by setting the voltage at the time of white gradation for each sample cell assuming that the transmittance with respect to the transmittance in the off state is 90%.
[0150]
From Table 5, when the voltage at the time of the white gradation is set with the transmittance being 90%, the sample cells # 3 and # 4 with the pretilt angles of 4.0 ° and 5.0 ° have the viewing angle of 70 ° and the opposite. Even when viewed from the viewing angle direction, no gradation inversion was confirmed, and the image quality was good.
[0151]
In sample cell # 5 with a pretilt angle of 10.0 °, good image quality was obtained up to a viewing angle of 50 °, but it was confirmed that the brightness was reduced when viewed from a normal viewing angle direction at a viewing angle of 60 °. However, this decrease in luminance was of a level that could be used. In sample cell # 2 in which the pretilt angle was 3.0 °, tone reversal was not confirmed even when viewed from the anti-viewing angle direction up to a viewing angle of 60 °, and good image quality was obtained. Was. However, there was no gradation inversion, and it was of a level that could be used. In sample cell # 6 in which the pretilt angle was 11.0 °, it was confirmed that the brightness was reduced when viewed from the normal viewing angle direction at a viewing angle of 50 °. there were. In sample cell # 1 with a pretilt angle of 2.0 °, the gray scale collapsed at a viewing angle of 50 ° and the gray scale was inverted at a viewing angle of 60 °, but it was of a degree that could be used.
[0152]
On the other hand, in sample cell # 7 in which the pretilt angle was 12.0 °, even at a viewing angle of 50 °, a decrease in luminance was found that was unusable when viewed from the normal viewing angle direction.
[0153]
[Table 6]

[0154]
Table 6 shows the results obtained by setting the voltage at the time of white gradation for each sample cell assuming that the transmittance with respect to the transmittance in the off state is 87%.
[0155]
From Table 6, when the voltage at the time of white gradation is set with the transmittance being 87%, the sample cells # 2, # 3, # 4 with the pretilt angles of 3.0 °, 4.0 °, and 5.0 ° are set. It was confirmed that the image quality was good up to a viewing angle of 50 °, but the brightness was reduced when viewed from a normal viewing angle direction at a viewing angle of 60 °. However, this decrease in luminance was of a level that could be used. At a viewing angle of 70 °, it was confirmed that the brightness decreased so as to be unusable when viewed from the normal viewing angle direction.
[0156]
In sample cell # 5 having a pretilt angle of 10.0 °, it was confirmed that the brightness was reduced when viewed from the normal viewing angle direction at a viewing angle of 50 ° and a viewing angle of 60 °, but it was of a degree that could withstand use. there were. At a viewing angle of 70 °, it was confirmed that the brightness decreased so as to be unusable when viewed from the normal viewing angle direction.
[0157]
In sample cells # 6 and # 7 in which the pretilt angles were 11.0 ° and 12.0 °, even at a viewing angle of 50 °, a decrease in luminance was found that was unusable when viewed from the normal viewing angle direction. .
[0158]
In sample cell # 1 with a pretilt angle of 2.0, tone reversal was not observed when viewed from the opposite viewing angle direction up to a viewing angle of 50 °, and good image quality was obtained. However, when viewed from the normal viewing angle direction at a viewing angle of 60 °. In this case, a decrease in luminance was confirmed. However, it was of such a degree that it could be used. At a viewing angle of 70 °, it was confirmed that the brightness decreased so as to be unusable when viewed from the normal viewing angle direction.
[0159]
[Table 7]

[0160]
Table 7 shows the results obtained by setting the voltage at the time of white gradation for each sample cell assuming that the transmittance with respect to the transmittance in the off state is 85%.
[0161]
From Table 7, when the voltage at the time of white gradation is set with the transmittance being 85%, the pretilt angles are 3.0 °, 4.0 °, 5.0 °, 10.0 °, 11.0 °, and 12 °. In the sample cells # 2, # 3, # 4, # 5, # 6, and # 7 that were set to 0.0 °, they were unusable when viewed from the normal viewing angle direction and the left-right direction even at a viewing angle of 50 °. A decrease in luminance was confirmed.
[0162]
On the other hand, in sample cell # 1 having a pretilt angle of 2.0, a decrease in luminance was observed when viewed from the normal viewing angle direction at a viewing angle of 50 °, but was acceptable for use. At a viewing angle of 60 °, it was confirmed that the brightness decreased so as to be unusable when viewed from the normal viewing angle direction.
[0163]
That is, from Tables 1 to 7, it can be said that adjusting the pretilt angle or adjusting the transmittance at the time of white gradation can improve the gradation inversion in the anti-viewing angle direction. In this case, when the transmittance of white gradation is set to about 95 to 97%, which is usually set, the pretilt angle is set to a range of more than 2 ° and less than 12 °, so that the gradation inversion in the anti-viewing angle direction at a viewing angle of 50 ° is performed. It can be said that the display can be improved and the display can be performed favorably without a decrease in luminance in the normal viewing angle direction. Further, by setting the angle in the range of 4 ° or more and 10 ° or less, even at a wide viewing angle of 70 °, gradation reversal in the anti-viewing angle direction is improved, and good display without luminance reduction in the normal viewing angle direction is achieved. It can be said that it can be done.
[0164]
Further, at a pretilt angle of 2 ° to 10 ° which is normally set, by obtaining a transmittance larger than 85% as a transmittance at the time of white gradation, gradation inversion in the anti-viewing angle direction at a viewing angle of 50 ° is performed. It can be said that the display can be improved and the display can be performed favorably without a decrease in luminance in the normal viewing angle direction. Further, by adjusting the pretilt angle by obtaining a transmittance in the range of 90% or more and 97% or less, gradation reversal in the anti-viewing angle direction is improved even at a wide viewing angle of 70 °. In addition, it can be said that good display can be achieved without luminance decrease in the normal viewing angle direction.
[0165]
Further, it can be said that by combining the adjustment of the pretilt angle and the adjustment of the transmittance at the time of white gradation, the effect of further improvement can be obtained.
[0166]
Next, for the same sample cell # 1 and sample cell # 4 as described above, the viewing angle of the liquid crystal display device was measured using a measuring system including a light receiving element 21, an amplifier 22, and a recording device 23 as shown in FIG. Dependencies were investigated.
[0167]
In this measurement system, the liquid crystal cell 16 of the liquid crystal display device is installed such that the surface 16a on the glass substrate 9 side is located on the reference plane XY of the orthogonal coordinates XYZ. The light receiving element 21 is an element capable of receiving light at a constant three-dimensional light receiving angle, and is arranged at a position at a predetermined distance from the coordinate origin in a direction forming an angle φ (viewing angle) with respect to a Z direction perpendicular to the surface 16a. ing.
[0168]
At the time of measurement, the liquid crystal cell 16 installed in the present measurement system is irradiated with monochromatic light having a wavelength of 550 nm from the surface opposite to the surface 16a. Part of the monochromatic light transmitted through the liquid crystal cell 16 enters the light receiving element 21. After the output of the light receiving element 21 is amplified to a predetermined level by the amplifier 22, it is recorded by a recording device 23 such as a waveform memory and a recorder.
[0169]
Here, the output level of the light receiving element 21 with respect to the voltage applied to the sample cells # 1 and # 4 when the light receiving element 21 was fixed at a fixed angle φ was measured.
[0170]
In the measurement, the light receiving element 21 is arranged at an angle φ of 50 °, assuming that the Y direction is the left side of the screen and the X direction is the lower side of the screen (normal viewing angle direction). The positions were changed in the upward direction (anti-viewing angle direction), the downward direction (normal viewing angle direction), and the left-right direction.
[0171]
The results are shown in FIGS. FIGS. 7A to 7C show the light transmittance (transmission) with respect to the voltage applied to the sample cell # 4 having a pretilt angle of 5.0 ° and the sample cell # 1 having the pretilt angle of 2.0 °. 6 is a graph showing the ratio of the applied voltage to the applied voltage of the liquid crystal.
[0172]
7A shows the result of measurement from above in FIG. 2, FIG. 7B shows the result of measurement from below in FIG. 2, and FIG. 7C shows the result from left and right.
[0173]
In FIG. 7A, a curve L1 indicated by a one-dot chain line is a result measured from the front, that is, the normal direction of the surface, and the sample cell # 1 and # 4 have the same transmittance-liquid crystal applied voltage characteristic.
[0174]
In FIGS. 7A to 7C, L2, L4, and L6 indicated by solid lines correspond to the sample cell # 4, and the curves L3, L5, and L7 indicated by broken lines correspond to the sample cell # 1.
[0175]
When comparing the upward transmittance-liquid crystal applied voltage characteristics of the sample cell # 4 and the sample cell # 1, from FIG. 7A, the curve L3 of the sample cell # 1 is missing from around 1V to around 2V. The curve L2 of the sample cell # 4 has a substantially constant transmittance due to the lack of the area near 1V to about 2V, whereas the hump disappears. Was not found.
[0176]
7 (b) and 7 (c), when comparing the transmittance and liquid crystal applied voltage characteristics in the downward direction and the horizontal direction, the curves L4 and L6 of the sample cell # 4 are respectively the curves L5 and L7 of the sample cell # 1. 7B, the transmittance of the sample cell # 4 decreases from about 2.5 V in FIG. 7B and from about 3 V in FIG. 7C. And it can be confirmed that there is no adverse effect of increasing the pretilt angle to 5.0 °.
[0177]
In addition, except that the discotic liquid crystal was hybrid-aligned on a transparent support as the optical retardation plates 2 and 3, the same as the above sample cells # 1 to # 7 was applied to the same sample cells. The result was obtained.
[0178]
(Example 1)
The present example is to confirm the effects of the liquid crystal display device according to the first and second reference examples and the embodiment, and here, the liquid crystal cell 16 in the liquid crystal display device of FIG. Optmer AL (trade name) manufactured by Nippon Synthetic Rubber Co., Ltd. was used for the alignment films 11 and 14. The pretilt angle was 3 ° with respect to the alignment films 11 and 14, and the refractive index anisotropy Δn (550 at a wavelength of 550 nm) was used. ) Are liquid crystal materials set to 0.070, 0.080, and 0.095 for the liquid crystal layer 8 and the cell thickness (thickness of the liquid crystal layer 8) is 5 μm. 18 were prepared.
[0179]
Here, the pretilt angle was measured using a pretilt angle measuring device NSMAP-3000, in which a homogeneous cell in which the materials of the sample cells # 16 to # 18 were injected was prepared.
[0180]
Further, as the optical retardation plates 2 and 3 in these sample cells # 16 to # 18, the same optical retardation plates 2 and 3 in Comparative Example 1 described above, in which discotic liquid crystals were tilted and aligned, were used.
[0181]
Then, using the measurement system shown in FIG. 6 similar to that described in the first embodiment, the voltage applied to the sample cells # 16 to # 18 when the light receiving element 21 is fixed at a fixed angle φ. The output level of the light receiving element 21 was measured.
[0182]
In the measurement, as in Reference Example 1, the light receiving element 21 is arranged so as to have an angle φ of 50 °, and the Y direction is the left side of the screen, and the X direction is the lower side of the screen (normal viewing angle direction). Assuming that the arrangement position of the light receiving element 21 was changed in the upward direction (opposite viewing angle direction), the downward direction (normal viewing angle direction), and the left and right direction, respectively.
[0183]
The results are shown in FIGS. FIGS. 8A to 8C are graphs showing the light transmittance (transmittance-liquid crystal applied voltage characteristic) with respect to the voltage applied to the sample cells # 16 to # 18.
[0184]
FIG. 8A shows the result of measurement from above in FIG. 2, FIG. 8B shows the result of measurement from the right in FIG. 2, and FIG. 8C shows the result from left.
[0185]
8A to 8C, curves L8, L11, and L4 indicated by alternate long and short dash lines respectively indicate sample cells # 16 using a liquid crystal material of Δn (550) = 0.070 in the liquid crystal layer 8, Curves L9, L12, and L15 indicated by solid lines are those of sample cell # 17 using a liquid crystal material of Δn (550) = 0.080 for liquid crystal layer 8, and curves L10, L13, and L16 indicated by broken lines are curves of liquid crystal layer 8. 8 is a sample cell # 18 using a liquid crystal material of Δn (550) = 0.095.
[0186]
As a comparative example with respect to the present embodiment, a liquid crystal material in which the refractive index anisotropy Δn (550) at a wavelength of 550 nm is set to 0.060 and 0.120, respectively, in the liquid crystal layer 8 in the liquid crystal cell 16 of FIG. Two comparative sample cells # 103 and # 104 were prepared in the same manner as in the present embodiment except that they were used, and they were installed in the measurement system shown in FIG. The output level of the light receiving element 21 with respect to the voltage applied to the comparative sample cells # 103 and # 104 when the angle was fixed at φ was also measured.
[0187]
In the measurement, as in the present embodiment, the light receiving element 21 is arranged so as to have an angle φ of 50 °, and the Y direction is the left side of the screen, and the X direction is the lower side of the screen (normal viewing angle direction). Assuming that the arrangement position of the light receiving element 21 was changed in the upward direction (anti-viewing angle direction), the right direction, and the left direction, respectively.
[0188]
The results are shown in FIGS. FIGS. 9A to 9C are graphs showing the light transmittance (transmittance-liquid crystal applied voltage characteristic) with respect to the voltage applied to the comparative example samples # 103 and # 104.
[0189]
FIG. 9A shows the result of measurement from above in FIG. 2, FIG. 9B shows the result of measurement from the right in FIG. 2, and FIG. 9C shows the result from left. .
[0190]
9A to 9C, curves L17, L19, and L21 indicated by solid lines are those of a comparative sample cell # 103 using a liquid crystal material of Δn (550) = 0.060 for the liquid crystal layer 8, Curves L18, L20, and L22 indicated by broken lines are those of a comparative sample cell # 104 using a liquid crystal material having a Δn (550) of 0.120 for the liquid crystal layer 8.
[0191]
When the upward transmittance-liquid crystal applied voltage characteristics of the sample cells # 16 to # 18 and the comparative sample cells # 103 and # 104 are compared, in FIG. It was confirmed that the transmittance was sufficiently reduced as the voltage was increased. On the other hand, in FIG. 9A, the transmittance of the curve L18 is not sufficiently reduced even when the voltage is increased, as compared with the curves L8, L9, and L10 of FIG. 8A. In the curve L17, an inversion phenomenon in which the transmittance once decreased with increasing voltage and then increased again was confirmed.
[0192]
Similarly, when comparing the transmittance in the right direction and the voltage applied to the liquid crystal for the sample cells # 16 to # 18 and the sample cells # 103 and # 104 for comparison, the curves L11, L12,. It was confirmed that as the voltage of L13 was increased, the transmittance decreased to almost zero. Also, in FIG. 9B, the curve L19 decreases as the voltage increases, as in FIG. 8B, until the transmittance becomes almost close to zero. confirmed.
[0193]
Similarly, for the sample cells # 16 to # 18 and the comparison sample cells # 103 and # 104, it was confirmed that the same was true in the left direction as in the right direction.
[0194]
Further, the sample cells # 16 to # 18 and the comparative sample cells # 103 and # 104 were visually checked under white light.
[0195]
Regarding the sample cells # 16 to # 18 and the sample cell # 103 for comparison, no color was observed and the image quality was good when viewed from any direction with a viewing angle of 50 °. On the other hand, it was confirmed that the comparative sample cell # 104 was colored from yellow to orange when viewed from the left and right directions at a viewing angle of 50 °.
[0196]
From the above results, as shown in FIGS. 8A to 8C, the liquid crystal layer 8 has the refractive index anisotropy Δn (550) at a wavelength of 550 nm of 0.070, 0.080, and 0.095, respectively. When a liquid crystal material set to is used, the transmittance decreases sufficiently as the voltage is applied, and no reversal phenomenon is observed. It can be seen that the display quality of the device is significantly improved.
[0197]
On the other hand, as shown in FIGS. 9A to 9C, the liquid crystal layer 8 has a liquid crystal layer 8 in which the refractive index anisotropy Δn (550) at a wavelength of 550 nm is set to 0.060 and 0.120, respectively. It is understood that the viewing angle dependency is not sufficiently improved when the material is used.
[0198]
Further, the same as the sample cells # 16 to # 18 and the sample cells # 103 and # 104 for comparison, except that the discotic liquid crystal was hybrid-aligned on a transparent support as the optical retardation plates 2 and 3. The same result was obtained for the sample cell and the sample cell for comparison.
[0199]
Also, the inclination angle θ of the refractive index ellipsoids of the optical retardation plates 2 and 3 was changed, and as a result of examining the dependence of the transmittance-liquid crystal applied voltage characteristic on the inclination angle θ, 15 ° ≦ θ ≦ 75 ° Within the range, there was basically no change irrespective of the state of orientation of the discotic liquid crystal in the optical retardation plates 2 and 3. In addition, it was confirmed that the viewing angle in the anti-viewing angle direction did not increase when the value exceeded the above range.
[0200]
Further, as a result of examining the dependency of the transmittance-liquid crystal applied voltage characteristic on the second retardation value by changing the second retardation value of the optical retardation plates 2 and 3, it was found that the second retardation value was 80 nm or less. Within the range of 250 nm, there was basically no change irrespective of the state of orientation of the discotic liquid crystal in the retardation plates 2 and 3. In addition, it was confirmed that the viewing angle in the left-right direction did not widen when exceeding the above range.
[0201]
The refractive index anisotropy Δn (550) at a wavelength of 550 nm of the liquid crystal layer 8 in the liquid crystal cell 16 of FIG. , 0.100, and 0.115 were prepared, and three sample cells # 19 to # 21 were prepared in the same manner as in the present example, and using the measurement system shown in FIG. In the same manner, the output level of the light receiving element 21 with respect to the voltage applied to the sample cells # 19 to # 21 when the light receiving element 21 was fixed at a fixed angle φ was measured. In addition, visual confirmation was performed under white light.
[0202]
As a result, in sample cell # 20 in which the refractive index anisotropy Δn (550) was 0.100, and in sample cell # 21 in which the refractive index anisotropy Δn (550) was 0.115, the angle was φ50 °. In this case, a slight increase in transmittance was confirmed when the voltage was increased in the left-right direction. However, the reversal phenomenon did not occur visually, and this increase in transmittance was acceptable for use. There was no problem in the upward result. On the other hand, in the sample cell # 19 in which the refractive index anisotropy Δn (550) is 0.065, similarly to the comparative sample cell # 103, when the voltage is increased in the upward direction, the transmittance once sinks and rises. However, the degree of increase in transmittance was smaller than that of the comparative sample cell # 103 shown in FIG. There were no problems with the results in the left-right direction.
[0203]
Further, in the visual inspection, in the sample cells # 20 and # 21, slight coloring from yellow to orange was confirmed, but this was not a problem. It was confirmed that sample cell # 19 exhibited a slight bluish color. However, this degree of blueness was not a problem.
[0204]
As a supplement, a voltage of about 1 V was applied to the sample cell # 19 and the comparative sample cell # 103, and the transmittance of the surface of the liquid crystal cell 16 at the time of white display in the normal direction was measured. As a result, in the comparative sample cell # 103, a decrease in the transmittance that was not endurable was observed. On the other hand, in the sample cell # 19, although a slight decrease in transmittance was confirmed, it was of a level that could be used.
[0205]
Further, Optmer AL (trade name) manufactured by Nippon Synthetic Rubber Co., Ltd. was used for the alignment films 11 and 14 of the liquid crystal cell 16 in the liquid crystal display device shown in FIG. 1, and the pretilt angles of the alignment films 11 and 14 were 4 ° and 5 °. Similar results were obtained also when liquid crystal materials having angles of 10 °, 10 °, and 11 ° were used for the liquid crystal layer 8, respectively.
[0206]
(Example 2)
This example is to confirm the effect of the liquid crystal display device according to the above embodiment. Here, the liquid crystal layer 8 of the liquid crystal cell 16 in the liquid crystal display device of FIG. Anisotropy Δn _L (450) and refractive index anisotropy Δn at a wavelength of 550 nm _L (550) and the refractive index anisotropy Δn of the optical retardation plates 2 and 3 at a wavelength of 450 nm. _F (450) and refractive index anisotropy Δn at a wavelength of 550 nm _F The relationship expressed by equation (1) with (550) uses a liquid crystal material and an optical retardation plate set to 0, 0.15, 0.25, 0.30, and 0.33, respectively. Five sample cells # 31 to # 35 having a cell thickness (thickness of the liquid crystal layer 8) of 5 μm were prepared.
[0207]
(Equation 15)

[0208]
As the optical retardation plates 2 and 3 in the sample cells # 31 to # 35, a discotic liquid crystal is applied to a transparent support (for example, triacetyl cellulose (TAC), etc.), and the discotic liquid crystal is tilted and cross-linked. The first retardation value described above is 0 nm, the second retardation value is 100 nm, and the main refractive index n _b Is inclined so as to be about 20 ° in the direction indicated by arrow A with respect to the z-axis direction in the xyz-axis coordinates, and similarly, the main refractive index n _c Has an angle of about 20 ° with respect to the x-axis in the direction shown by the arrow B (that is, the index ellipsoid has an inclination angle θ = 20 °).
[0209]
As a comparative example with respect to the present embodiment, the relationship represented by the above equation (1) is 0.35, 1.0, 1.... In the liquid crystal layer 8 of the liquid crystal cell 16 in the liquid crystal display device of FIG. Comparative sample cells # 301 to # 303 were prepared in the same manner as in this example except that the liquid crystal material of No. 1 and the optical retardation plate were used.
[0210]
Table 8 shows the results of a visual test performed on the above sample cells # 31 to # 35 and the comparative sample cells # 301 to # 303 under white light.
[0211]
[Table 8]

[0212]
Regarding the sample cells # 31 to # 33, no coloring was observed from any direction with a viewing angle of 70 °, and good image quality was obtained. In the sample cell # 24, no coloring was observed from any direction up to a viewing angle of 50 °, and good image quality was obtained. However, at a viewing angle of 60 °, slight coloring was observed when viewed from the left and right directions. It was colored enough to withstand use. In the sample cell # 25, coloring was not observed from any direction up to a viewing angle of 50 °, and the image quality was good. However, at a viewing angle of 60 °, coloring that would not withstand use when viewed from the left and right directions was observed. confirmed.
[0213]
On the other hand, in the comparative sample cells # 301 to # 303, even when viewed from the left and right directions even at a viewing angle of 50 °, a yellow to orange color that was unusable was confirmed.
[0214]
Further, the same as the sample cells # 31 to # 35 and the sample cells # 301 to # 303 of the present example, except that the discotic liquid crystal was hybrid-aligned on a transparent support as the optical retardation plates 2 and 3. The same result as described above was obtained for the sample cell and the comparative sample cell.
[0215]
(Example 3)
The present example is to confirm the effect of the liquid crystal display device according to the third embodiment. Here, the liquid crystal layer 8 of the liquid crystal cell 16 in the liquid crystal display device of FIG. 1 has a refractive index at a wavelength of 550 nm. Anisotropy Δn _L (550) and refractive index anisotropy Δn at a wavelength of 650 nm _L (650) and the refractive index anisotropy Δn at a wavelength of 550 nm of the optical retardation plates 2 and 3 _F (550) and refractive index anisotropy Δn at a wavelength of 650 nm _F The relationship expressed by the equation (2) with (650) uses a liquid crystal material and an optical retardation plate set to 0, 0.10, 0.20, 0.23, and 0.25, respectively. Five sample cells # 41 to # 45 having a cell thickness (thickness of the liquid crystal layer 8) of 5 μm were prepared.
[0216]
(Equation 16)

[0219]
As the optical retardation plates 2 and 3 in the sample cells # 41 to # 45, a discotic liquid crystal is applied to a transparent support (for example, triacetyl cellulose (TAC) or the like), and the discotic liquid crystal is tilted and crosslinked. The first retardation value described above is 0 nm, the second retardation value is 100 nm, and the main refractive index n _b Is inclined so as to be about 20 ° in the direction indicated by arrow A with respect to the z-axis direction in the xyz-axis coordinates, and similarly, the main refractive index n _c Has an angle of about 20 ° with respect to the x-axis in the direction shown by the arrow B (that is, the index ellipsoid has an inclination angle θ = 20 °).
[0218]
As a comparative example with respect to the present embodiment, the relationship represented by the above equation (2) in the liquid crystal layer 8 of the liquid crystal cell 16 in the liquid crystal display device of FIG. Comparative sample cells # 401 to # 403 were prepared in the same manner as in this example except that the liquid crystal material of No. 1 and the optical retardation plate were used.
[0219]
Table 9 shows the results of a visual test performed on the sample cells # 41 to # 45 and the comparative sample cells # 401 to # 403 under white light.
[0220]
[Table 9]

[0221]
With respect to the sample cells # 41 to # 43, coloring was not observed when viewed from any direction with a visual angle of 70 °, and the image quality was good. In sample cell # 44, no coloring was observed from any direction up to a viewing angle of 50 °, and good image quality was obtained. However, at a viewing angle of 60 °, slight coloring was observed when viewed from the left and right directions. It was colored enough to withstand use. In the sample cell # 45, a slight coloring was observed when viewed from the left and right directions at a viewing angle of 50 °, but the coloring was such that it could be used.
[0222]
On the other hand, in the comparative sample cells # 401 to # 403, when viewed from the left and right directions even at a viewing angle of 50 °, coloring from yellow to orange that was unusable was confirmed.
[0223]
The same as the sample cells # 41 to # 45 and the comparative sample cells # 401 to # 403 of the present example, except that the discotic liquid crystal was hybrid-aligned on a transparent support as the optical retardation plates 2 and 3. The same result as described above was obtained for the sample cell and the comparative sample cell.
[0224]
【The invention's effect】
As described above, in the first liquid crystal display device according to the present invention, the liquid crystal layer twisted by approximately 90 ° between the pair of light-transmitting substrates each having the transparent electrode layer and the alignment film formed on the opposing surfaces is provided. , A pair of polarizers disposed on both sides of the liquid crystal display device, and at least one optical retardation plate interposed between the liquid crystal display device and the polarizer. And the three main refractive indices n of the index ellipsoid _a , N _b , N _c Is n _a = N _c > N _b And the main refractive index n in the surface _a Or n _c The principal refractive index n parallel to the surface normal direction with the direction of _b And the main refractive index n in the surface _c Or n _a Is tilted clockwise or counterclockwise to provide an optical retardation plate in which the refractive index ellipsoid is tilted, and the liquid crystal material in the liquid crystal layer has a wavelength of 450 nm for light. Refractive index anisotropy Δn _L (450) and refractive index anisotropy Δn for light having a wavelength of 550 nm _L Δn which is the ratio of (550) _L (450) / Δn _L (550) and the refractive index anisotropy Δn of the optical retardation plate with respect to light having a wavelength of 450 nm. _F (450) and refractive index anisotropy Δn for light having a wavelength of 550 nm _F Δn which is the ratio of (550) _F (450) / Δn _F (550)
[0225]
[Equation 17]

[0226]
Is set so as to satisfy the following relationship.
[0227]
Further, as a more preferable configuration,
[0228]
(Equation 18)

[0229]
Is set so as to satisfy the following relationship.
[0230]
In a second liquid crystal display device according to the present invention, a liquid crystal layer that is twisted and aligned by approximately 90 ° is sealed between a pair of translucent substrates each having a transparent electrode layer and an alignment film formed on opposing surfaces. A liquid crystal display element, a pair of polarizers disposed on both sides of the liquid crystal display element, and an optical retardation plate interposed at least one between the liquid crystal display element and the polarizer, wherein a refractive index ellipse is provided. The three principal refractive indices n of the body _a , N _b , N _c Is n _a = N _c > N _b And the main refractive index n in the surface _a Or n _c The principal refractive index n parallel to the surface normal direction with the direction of _b And the main refractive index n in the surface _c Or n _a Is tilted clockwise or counterclockwise to provide an optical retardation plate in which the refractive index ellipsoid is tilted, and that the liquid crystal material in the liquid crystal layer has a wavelength of 650 nm. Refractive index anisotropy Δn _L (650) and refractive index anisotropy Δn for light having a wavelength of 550 nm _L Δn which is the ratio of (550) _L (650) / Δn _L (550) and the refractive index anisotropy Δn of the optical retardation plate for light having a wavelength of 650 nm. _F (650) and refractive index anisotropy Δn for light having a wavelength of 550 nm _F Δn which is the ratio of (550) _F (650) / Δn _F (550)
[0231]
[Equation 19]

[0232]
Is set so as to satisfy the following relationship.
[0233]
Further, as a more preferable configuration,
[0234]
(Equation 20)

[0235]
Is set so as to satisfy the following relationship.
[0236]
As a result, in the first and second liquid crystal display devices according to the present invention, the change in the phase difference of the liquid crystal display element is further improved as compared with the case where only the compensation function is provided by the phase difference plate, and in particular, the coloring of the liquid crystal screen depending on the viewing angle. Since the phenomenon can be further prevented, the liquid crystal display device including such a phase difference plate and a liquid crystal display element can prevent a reversal phenomenon, a decrease in contrast ratio in a viewing angle direction, and a coloring phenomenon.
[0237]
Therefore, the above configuration has an effect that the quality of the display image of the liquid crystal display device is remarkably improved because the contrast ratio in the black and white display is not affected by the viewing angle direction of the viewer.
[0238]
In each of the liquid crystal display devices according to the invention described above, the refractive index anisotropy Δn (550) of the liquid crystal material in the liquid crystal layer with respect to light having a wavelength of 550 nm is set to a range larger than 0.060 and smaller than 0.120. It is preferred that
[0239]
Accordingly, since a phase difference corresponding to a viewing angle generated in the liquid crystal display element can be eliminated, not only a coloring phenomenon depending on the viewing angle but also a contrast change, a left-right inversion phenomenon, and the like on the display screen. Can be improved.
[0240]
In this case, it is preferable that the refractive index anisotropy Δn (550) of the liquid crystal material in the liquid crystal layer with respect to light having a wavelength of 550 nm is set in the range of 0.070 or more and 0.095 or less.
[0241]
As a result, it is possible to further improve the contrast change and the left-right reversal phenomenon that occur depending on the viewing angle.
[0242]
In each of the liquid crystal display devices according to the present invention described above, it is preferable that the inclination angle of the refractive index ellipsoid is set between 15 ° and 75 ° in all of the retardation plates.
[0243]
As described above, in all the optical retardation plates interposed in the liquid crystal display device, by setting the inclination angle of the refractive index ellipsoid between 15 ° and 75 °, the above-described optical retardation provided by the present invention is provided. The function of compensating for the phase difference by the plate can be reliably obtained, and the visibility can be reliably improved.
[0244]
In each of the liquid crystal display devices according to the present invention described above, the main refractive index n _a And the main refractive index n _b (N) and the thickness d of the optical retardation plate (n _a -N _b ) × d is preferably set between 80 nm and 250 nm.
[0245]
Thus, in all the optical retardation plates interposed in the liquid crystal display device, the main refractive index n _a And the main refractive index n _b (N) and the thickness d of the optical retardation plate (n _a -N _b By setting (x) between 80 nm and 250 nm, the function of compensating for the phase difference by the optical retardation plate of the present invention described above can be reliably obtained, and the visibility can be reliably improved.
[Brief description of the drawings]
FIG. 1 is an exploded cross-sectional view illustrating a configuration of a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a relationship between a rubbing direction of an alignment film and a normal viewing angle direction in the liquid crystal display device.
FIG. 3 is a perspective view showing a main refractive index in an optical retardation plate of the liquid crystal display device.
FIG. 4 is a perspective view showing an optical arrangement of a polarizing plate and an optical retardation plate in the liquid crystal display device by disassembling respective parts of the liquid crystal display device.
FIG. 5 is an explanatory diagram showing a pretilt angle which is an angle formed between a long axis of liquid crystal molecules and an alignment film.
FIG. 6 is a perspective view showing a measurement system for measuring the viewing angle dependency of the liquid crystal display device.
FIG. 7 is a graph showing transmittance-liquid crystal applied voltage characteristics of the liquid crystal display devices of Comparative Example 1 and Comparative Example 1 with respect to Comparative Example 1.
FIG. 8 is a graph showing transmittance-liquid crystal applied voltage characteristics of the liquid crystal display device in Example 1.
FIG. 9 is a graph showing transmittance-liquid crystal applied voltage characteristics of a liquid crystal display device of a comparative example with respect to Example 1.
FIG. 10 is a graph showing Δn (λ) / Δn (550) with respect to the wavelength of one liquid crystal material and one optical retardation plate used for the liquid crystal layer of the liquid crystal display device.
FIG. 11 is a schematic diagram showing a twist alignment of liquid crystal molecules in a TN liquid crystal display element.
[Explanation of symbols]
1 Liquid crystal display device
2.3 Optical retardation plate
4.5 Polarizing plate (polarizer)
8 Liquid crystal layer
9.12 Glass substrate (translucent substrate)
10.13 Transparent electrode (transparent electrode layer)
11.14 Alignment film

Claims (8)

A liquid crystal display element in which a liquid crystal layer that is twisted and oriented substantially 90 ° is sealed between a pair of translucent substrates each having a transparent electrode layer and an alignment film formed on opposing surfaces,
A pair of polarizers disposed on both sides of the liquid crystal display element,
An optical retardation plate interposed between the liquid crystal display element and the polarizer, wherein at least one of the three main refractive indices n _a , n _b , and n _{c of the} index ellipsoid is n _a = n _c. > has the relationship of n _b, a direction of the principal refractive index n _a or n _c in the surface as an axis, the direction of the principal refractive index n _b parallel to the direction normal to the surface, the main refractive index in the surface n by the direction of the _c or n _a is inclined clockwise or counterclockwise, and an optical retardation plate in which the refractive index ellipsoid is inclined,
And, the liquid crystal material in the liquid crystal layer, which is the ratio of the refractive index anisotropy [Delta] n _L (550) the refractive index anisotropy [Delta] n _L and (450) of wavelength 550nm to light with respect to light having a wavelength of 450 nm [Delta] n _L (450) / Δn _L (550), Δn which is the ratio of the refractive index anisotropy Δn _F (450) of the optical retardation plate to light having a wavelength of 450 nm and the refractive index anisotropy Δn _F (550) of light having a wavelength of 550 nm. _F (450) / Δn _F (550)

The liquid crystal display device is set so as to satisfy the following relationship. ΔnL (450) / ΔnL (550), which is the ratio of the refractive index anisotropy ΔnL (450) of the liquid crystal material in the liquid crystal layer to light having a wavelength of 450 nm and the refractive index anisotropy ΔnL (550) to light having a wavelength of 550 nm. ΔnF (450) / ΔnF (550), which is the ratio of the refractive index anisotropy ΔnF (450) of the optical retardation plate to light having a wavelength of 450 nm and the refractive index anisotropy ΔnF (550) of light having a wavelength of 550 nm. But,

The liquid crystal display device according to claim 1, wherein the relationship is set so as to satisfy the following relationship. A liquid crystal display element in which a liquid crystal layer that is twisted and oriented substantially 90 ° is sealed between a pair of translucent substrates each having a transparent electrode layer and an alignment film formed on opposing surfaces,
A pair of polarizers disposed on both sides of the liquid crystal display element,
An optical retardation plate interposed between the liquid crystal display element and the polarizer, wherein at least one of the three main refractive indices n _a , n _b , and n _{c of the} index ellipsoid is n _a = n _c. > has the relationship of n _b, a direction of the principal refractive index n _a or n _c in the surface as an axis, the direction of the principal refractive index n _b parallel to the direction normal to the surface, the main refractive index in the surface n by the direction of the _c or n _a is inclined clockwise or counterclockwise, and an optical retardation plate in which the refractive index ellipsoid is inclined,
And, the liquid crystal material in the liquid crystal layer, which is the ratio of the refractive index anisotropy [Delta] n _L (550) the refractive index anisotropy [Delta] n _L and (650) of wavelength 550nm to light with respect to light having a wavelength of 650 nm [Delta] n _L (650) / Δn _L (550), the ratio of the refractive index anisotropy Δn _F (650) of the optical retardation plate to light having a wavelength of 650 nm and the refractive index anisotropy Δn _F (550) of light having a wavelength of 550 nm. _F (650) / Δn _F (550)

The liquid crystal display device is set so as to satisfy the following relationship. Δn _L (650) / Δn _L, which is the ratio of the refractive index anisotropy Δn _L (650) of the liquid crystal material in the liquid crystal layer to light having a wavelength of 650 nm and the refractive index anisotropy Δn _L (550) to light having a wavelength of 550 nm. and (550), Δn _F (650 is the ratio of the refractive index anisotropy [Delta] n _F (550) to the refractive index anisotropy [Delta] n _F (650) and a wavelength of 550nm light with respect to light having a wavelength of 650nm of the optical retardation plate ) / Δn _F (550)

The liquid crystal display device according to claim 3, wherein the relationship is set so as to satisfy the following relationship. The liquid crystal material in the liquid crystal layer has a refractive index anisotropy [Delta] n (550) for light having a wavelength of 550 nm set in a range larger than 0.060 and smaller than 0.120. The liquid crystal display device according to any one of the above. 6. The liquid crystal material according to claim 5, wherein the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (550) with respect to light having a wavelength of 550 nm in a range of 0.070 or more and 0.095 or less. Liquid crystal display. The liquid crystal display device according to any one of claims 1 to 6, wherein in all the optical retardation plates, the inclination angle of the refractive index ellipsoid is set between 15 ° and 75 °. In all of the optical phase difference plate, and the principal refractive index _{n a} and the difference between the principal refractive index _{n b,} a product _(n a -n _b) × d of the thickness d of the optical phase difference plate, 80 nm from 250nm of The liquid crystal display device according to claim 1, wherein the liquid crystal display device is set between them.

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